JPS6224499B2 - - Google Patents
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- Publication number
- JPS6224499B2 JPS6224499B2 JP53142180A JP14218078A JPS6224499B2 JP S6224499 B2 JPS6224499 B2 JP S6224499B2 JP 53142180 A JP53142180 A JP 53142180A JP 14218078 A JP14218078 A JP 14218078A JP S6224499 B2 JPS6224499 B2 JP S6224499B2
- Authority
- JP
- Japan
- Prior art keywords
- carbon
- carbide
- carbides
- temperature
- steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 84
- 229910052799 carbon Inorganic materials 0.000 claims description 84
- 238000005255 carburizing Methods 0.000 claims description 33
- 229910000831 Steel Inorganic materials 0.000 claims description 31
- 239000010959 steel Substances 0.000 claims description 31
- 150000001247 metal acetylides Chemical class 0.000 claims description 29
- 238000010438 heat treatment Methods 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 18
- 229910000851 Alloy steel Inorganic materials 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 7
- 229910000734 martensite Inorganic materials 0.000 claims description 7
- 229910001563 bainite Inorganic materials 0.000 claims description 5
- 229910001562 pearlite Inorganic materials 0.000 claims description 5
- 238000003303 reheating Methods 0.000 claims 1
- 239000002344 surface layer Substances 0.000 claims 1
- 229910001566 austenite Inorganic materials 0.000 description 26
- 239000000463 material Substances 0.000 description 14
- 239000000203 mixture Substances 0.000 description 11
- 238000010586 diagram Methods 0.000 description 9
- 239000003921 oil Substances 0.000 description 7
- 238000012360 testing method Methods 0.000 description 5
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 230000007423 decrease Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 150000001721 carbon Chemical class 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- 229910001339 C alloy Inorganic materials 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910000954 Medium-carbon steel Inorganic materials 0.000 description 1
- 101100202505 Saccharomyces cerevisiae (strain ATCC 204508 / S288c) SCM4 gene Proteins 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000010687 lubricating oil Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000010705 motor oil Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/20—Carburising
- C23C8/22—Carburising of ferrous surfaces
Description
本発明は、炭素量が0.5％以下の低中炭素低合
金鋼を浸炭処理することによつて鋼の表面付近に
多量の擬球状または球状の炭化物を生成させるこ
とができるようにした鋼の浸炭熱処理方法に関す
るものである。
従来の浸炭方法によつて鋼の表面に球状の炭化
物を生成させるためには鋼中のCr含有量を2.4％
以上にする必要があつた。鋼中にCrを2.4％以上
含む場合は、一定温度にてＡcmを越えるカーボン
ポテンシヤルの浸炭雰囲気中で浸炭を行えば、オ
ーステナイト結晶粒界、オーステナイト結晶粒内
にほぼ均一に球状炭化物が生成することは周知で
ある。しかるに、通常広く使用されているCr含
有量が２％以下の鋼については、一定温度にてＡ
cmを越えるカーボンポテンシヤルの浸炭雰囲気中
で浸炭を行つても網状または塊状の炭化物がオー
ステナイト結晶粒界に生成し、オーステナイト結
晶粒内には炭化物の生成が起らない。
このような組織は焼割れ、研削割れを起しやす
く、耐ピツチング性なども良くない。また、この
オーステナイト結晶粒界に網状または塊状に生成
した炭化物の球状化はほとんど不可能である。
本発明は以上のような背景のもとになされたも
のであり、その目的とする所は炭素量0.5％以
下、Cr量2.4％未満の低中炭素低合金鋼を浸炭す
ることにより、鋼の表面から深さ0.4mmまでの範
囲内に体積率が30％以上の擬球状または球状の炭
化物を生成させることができ、耐熱性、耐摩耗
性、耐ピツチング性が著しくすぐれた鋼にするこ
とができる浸炭熱処理方法を提供することであ
る。
第１図に本発明の熱処理サイクルを示す。すな
わち、
Ｃ：0.05〜0.50
Si：0.10〜0.35
Mn：0.30〜2.00
Ni：０〜5.50
Cr：０〜2.00
Mo：０〜0.70
（各含有成分は重量％以下同じ）
を含み、その他通常随伴される不純物元素を含
み、残部がFeよりなる低中炭素低合金鋼すなわ
ち肌焼鋼、機械構造用炭素鋼、機械構造用低合金
鋼を表面炭素量が共析以上となるように被処理鋼
のＡcm以下のカーボンポテンシヤルにて浸炭を行
い、空冷して浸炭層をベイナイトまたはパーライ
ト組織とするかまたは焼入れを行つてマルテンサ
イト組織とする（この浸炭工程を予備浸炭と称す
る）。予備浸炭後に品物の表面から深さ0.1〜0.4
mm（深さは鋼種、処理条件により異る）まで体積
率が30％以上の擬球状または球状の炭化物を生成
させるために、さらにAc1点以上の温度における
カーボンポテンシヤルがＡcmを越えるように維持
しつつ、Ac1点から750〜950℃の温度範囲まで品
物の表面における加熱速度が20℃／分以下となる
ように昇温する。そしてこの温度範囲にてＡcmを
越える高いカーボンポテンシヤルを維持しながら
適当時間浸炭を行う（この浸炭工程を炭化物生成
処理と称する）。
この炭化物生成処理を行なつた後は750〜950℃
の温度範囲から直接焼入を行なつてもよいし、残
留オーステナイトを少くするために、一たん空冷
してから酸化脱炭を起こさないような方法にて再
加熱焼入してもよい。
次に本発明によれば鋼中のCr量が2.4％未満で
も擬球状および球状の炭化物が多量に得られる理
由を説明する。周知のようにCr量が2.4％以上の
場合にカーボンポテンシヤルがＡcmを越えるよう
な浸炭雰囲気にて浸炭を行うと、多量の炭化物が
得られる理由は、Crが炭化物の核を作りやすい
元素であることと、鋼中のCr量が増加するに従
つて、鋼のＡcm線が低炭素側に移動することによ
り、オーステナイトの飽和炭素量を減少して炭化
物を作りやすくなることなどである。一方、Cr
量の少ない鋼の場合には、Ａcmを越えるような浸
炭雰囲気中にて浸炭を行なつても炭化物はオース
テナイト結晶粒内には生成せず、オーステナイト
結晶粒界に網状または塊状に生成することは前述
した通りである。しかるに本発明の熱サイクルの
ようにまず被処理鋼のＡcm以下のカーボンポテン
シヤルにて、品物の表面炭素量が共析以上となる
ように予備浸炭してから空冷または焼入して、
Ac1点から炭化物生成処理温度までの温度範囲を
被処理鋼のＡcmを越えるカーボンポテンシヤルを
維持しつつ品物の表面における加熱速度が20℃／
分以下となるように昇温して、炭化物生成処理温
度にて、Ａcmを越えるカーボンポテンシヤルを維
持しながら適当時間の浸炭を行えば、品物の表面
から深さ0.1〜0.4mmまで、体積率30％以上の擬球
状または球状炭化物が得られるのである。この理
由は次のようである。たとえば、予備浸炭時の表
面炭素量を共析組成とした場合について述べる。
予備浸炭後に空冷した場合、品物の表面付近はベ
イナイトまたはパーライト組織となつている。炭
化物生成処理において、品物の表面付近がAc1点
を越えると、ベイナイトまたはパーライトがオー
ステナイトに変態する。変態直後においてはオー
ステナイト中の炭素量は共析組成よりも低い。従
つてオーステナイト中には未溶解の炭化物が存在
する。この未溶解炭化物は時間の経過または温度
の上昇によつてオーステナイトに溶解する傾向に
ある。しかしながら、雰囲気のカーボンポテンシ
ヤルがＡcmを越えているので表面付近の不飽和の
オーステナイトは表面から炭素が拡散することに
より、速やかに飽和するから、未溶解炭化物はオ
ーステナイトに溶解せずに残存する。ただし、オ
ーステナイトの飽和炭素量は温度の上昇とともに
増加するので、Ac1点以上の加熱速度があまり速
いと、不飽和のオーステナイトが表面からの炭素
の拡散によつて飽和する速度よりも、未溶解炭化
物が不飽和のオーステナイトに溶解する速度の方
が速くなつて、炭化物はすべてオーステナイトに
溶解してしまう。この加熱速度の上限が20℃／分
である。
すなわち、Ac1点から、炭化物生成温度までの
温度範囲を、Ａcmを越えるカーボンポテンシヤル
を維持しながら、20℃／分以下の加熱速度にて昇
温し、炭化物生成温度にて適当時間保持すれば、
前記の未溶解炭化物が生長して、擬球状または球
状の炭化物となる。
予備浸炭後に焼入れして、マルテンサイト組織
とした場合は、炭化物処理時において、Ac1点に
昇温する途中でマルテンサイトが分解して球状炭
化物が生成するから、前述のようにこの球状炭化
物のうち、オーステナイトに未溶解のものが核と
なつて本発明の方法によれば主として球状炭化物
が生成する。
予備浸炭時の表面炭素量が過共析組成の場合に
はAc1点を越える温度にてオーステナイト化した
直後の未溶解炭化物の量は予備浸炭時の表面炭素
量が共析組成の場合よりも多い。従つて炭化物生
成処理後の炭化物の量は共析組成の場合よりも多
くなる。また、予備浸炭時の表面炭素量が過共析
組成の場合は、空冷するとオーステナイト結晶粒
界に細い網状炭化物が生成するが、この炭化物は
炭化物生成処理時の昇温途中において分断されて
球状となる。
予備浸炭時の表面炭素量が亜共析組成の場合
は、炭化物生成処理後の炭化物の体積率が30％以
下となるので耐熱性、耐摩耗性、耐ピツチング性
が、通常の浸炭品と比較して、あまり向上しな
い。従つて、予備浸炭時の表面炭素量は共析以上
とすることが必要である。また、予備浸炭時のカ
ーボンポテンシヤルがＡcmを越える（表面炭素量
がＡcmを越える）と、オーステナイト結晶粒界に
太い網状または塊状の炭化物が生成するので、予
備浸炭時のカーボンポテンシヤルはＡcmを越えて
はならない。
炭化物生成処理温度は低中炭素低合金鋼のAc1
点直上の750℃を下限とし、現用浸炭炉の耐用限
界および心部の結晶粒粗大化の観点から、950℃
を上限とする。
また、本発明の熱処理方法の対象となる鋼の炭
素含有量は0.5％を上限とする。これは、鋼の炭
素量が0.5％を越えると、炭化物層が0.05mm以下
となり、耐熱性、耐摩耗性、耐ピツチング性が低
下するためである。従つて、実用的にみれば、本
発明の熱処理方法の対象となる鋼は、低中炭素低
合金鋼となる。
実施例
第２図は浸炭鋼JIS SCM21（0.18C，0.21Si，
0.63Mn，0.011P，0.016S，0.07Ni，0.94Cr，
0.18Mo）およびJIS SNCM21（0.23C，0.27Si，
0.76Mn，0.014P，0.018S，0.45Ni，0.53Cr，
0.20Mo）をプロパン変成RXガスを使用して930
〜980℃の温度範囲にて0.06〜0.25％CO2（カーボ
ンポテンシヤル0.50〜1.48％）にて６〜12時間予
備浸炭後、空冷あるいは焼入して、Ac1から900
℃までＡcmを越えるカーボンポテンシヤル（たと
えば750℃では1.0％CO2、800℃では0.61％CO2、
850℃では0.25％CO2）を維持しつつ３℃／分の加
熱速度で昇温して、900℃、0.12％CO2（カーボ
ンポテンシヤル1.85％）にて６時間の炭化物生成
処理を行い油冷したものについて、品物の表面か
ら深さ0.1mmにおける炭化物体積率と予備浸炭時
の表面炭素量との関係を示したものである。
SCM21およびSNCM21の共析炭素量はほぼ0.78％
であり、予備浸炭温度（930℃）におけるＡcm炭
素量は1.30％である。炭化物の体積率が30％以下
になると、耐熱性、耐摩耗性、耐ピツチング性が
従来の浸炭法と比較してあまり向上しないので、
炭化物体積率の下限を30％とすると、予備浸炭時
の表面炭素量の下限は共析組成付近となる。ま
た、被処理鋼のＡcm線を越える表面炭素量の場合
には、オーステナイト結晶粒界に網状または塊状
の炭化物が生成するので好ましくない。従つて擬
球状あるいは球状の炭化物を生成させるための予
備浸炭時のカーボンポテンシヤルは共析以上Ａcm
以下となる。
第３図は第２図に用いたものと同一組成のJIS
SCM21、SNCM21浸炭鋼を930〜980℃の温度範
囲で0.18〜0.06％CO2（カーボンポテンシヤル
0.80〜1.30％）にて６〜12時間浸炭後空冷して、
Ac1から900℃までＡcmを越えるカーボンポテン
シヤルを維持しつつ品物の表面における加熱速度
を0.12〜30℃／分の範囲の種々の速度にて昇温
し、900℃，0.12％CO2（カーボンポテンシヤル
1.85％）にて６時間の炭化物生成処理を行つた品
物の表面から深さ0.1mmにおける炭化物の体積率
とAc1から900℃までの加熱速度との関係を示し
たものである。前述の理由で、炭化物体積率の下
限を30％とすると、加熱速度の上限は20℃／分付
近となる。また、加熱速度の下限は実用的観点か
らみれば0.3℃／分付近となろう。
第４図は、炭素量の異る種々の鋼（化学組成を
表に示す）を930℃の温度で0.13％CO2（カーボ
ンポテンシヤル1.07％）のRXガス中にて10時間
浸炭してから空冷してAc1点から850℃〜930℃ま
でＡcmを越えるカーボンポテンシヤルを維持しな
がら３℃／分の加熱速度で昇温して、この温度範
囲で0.25〜0.06％CO2（カーボンポテンシヤル
1.63〜2.10％）のRXガス中にて６時間浸炭後油
冷したものの炭化物層の厚さと素材の炭素量との
関係とを示したものである。素材の炭素量が0.5
％を越えると、炭化物層の厚さが0.05mm以下とな
り、耐熱性、耐摩耗性、耐ピツチング性が低下す
るので素材の炭素量の上限は0.5％付近となる。
素材の炭素量が高くなると炭化物層の厚さが薄く
なる理由は、素材の炭素量が高いほど浸炭雰囲気
のカーボンポテンシヤルと素材炭素量との差が小
さくなり、オーステナイト中の炭素の拡散速度が
遅くなるためと考えられる。
The present invention is a carburizing steel that is capable of producing a large amount of pseudospherical or spherical carbides near the surface of the steel by carburizing low-medium carbon low alloy steel with a carbon content of 0.5% or less. The present invention relates to a heat treatment method. In order to generate spherical carbides on the surface of steel using the conventional carburizing method, the Cr content in the steel must be 2.4%.
I needed to do more than that. When steel contains 2.4% or more of Cr, if carburizing is performed in a carburizing atmosphere with a carbon potential exceeding Acm at a constant temperature, spherical carbides will be generated almost uniformly at the austenite grain boundaries and within the austenite grains. is well known. However, for commonly used steels with a Cr content of 2% or less, A
Even if carburizing is performed in a carburizing atmosphere with a carbon potential exceeding cm, net-like or massive carbides are generated at the austenite grain boundaries, and no carbides are generated within the austenite grains. Such a structure is prone to quenching cracks and grinding cracks, and has poor pitting resistance. Furthermore, it is almost impossible to spheroidize the carbides formed in a network or block form at the austenite grain boundaries. The present invention has been made against the above background, and its purpose is to carburize low to medium carbon low alloy steel with a carbon content of 0.5% or less and a Cr content of less than 2.4%. Pseudo-spherical or spherical carbides with a volume fraction of 30% or more can be generated within a depth of 0.4 mm from the surface, making it possible to produce steel with extremely excellent heat resistance, wear resistance, and pitting resistance. The object of the present invention is to provide a carburizing heat treatment method that can be used. FIG. 1 shows the heat treatment cycle of the present invention. That is, C: 0.05 to 0.50 Si: 0.10 to 0.35 Mn: 0.30 to 2.00 Ni: 0 to 5.50 Cr: 0 to 2.00 Mo: 0 to 0.70 (Each component is the same below weight%), and other normally accompanying components. The Acm of the steel to be treated is made such that the surface carbon content of the low-medium carbon low alloy steel containing impurity elements and the balance being Fe, i.e., case hardening steel, carbon steel for machine structures, and low alloy steel for machine structures is eutectoid or higher. Carburizing is performed at the following carbon potential, and the carburized layer is air-cooled to form a bainite or pearlite structure, or quenched to form a martensitic structure (this carburizing step is referred to as preliminary carburizing). Depth 0.1~0.4 from the surface of the item after preliminary carburizing
In order to generate pseudospherical or spherical carbides with a volume fraction of 30% or more up to a depth of 30 mm (depth varies depending on the steel type and processing conditions), the carbon potential is maintained to exceed A cm at a temperature of 1 or more Ac. At the same time, the temperature is raised from Ac 1 point to a temperature range of 750 to 950°C such that the heating rate on the surface of the item is 20°C/min or less. Then, carburization is carried out in this temperature range for an appropriate period of time while maintaining a high carbon potential exceeding Acm (this carburization process is referred to as carbide generation treatment). After this carbide generation treatment, the temperature is 750 to 950℃.
Direct quenching may be performed from a temperature range of 1, or in order to reduce residual austenite, the material may be air cooled and then reheated and quenched using a method that does not cause oxidative decarburization. Next, the reason why a large amount of pseudospherical and spherical carbides can be obtained according to the present invention even when the Cr content in the steel is less than 2.4% will be explained. As is well known, when carburizing is performed in a carburizing atmosphere where the carbon potential exceeds Acm when the Cr content is 2.4% or more, a large amount of carbide is obtained.The reason why a large amount of carbide is obtained is that Cr is an element that easily forms carbide nuclei. In addition, as the amount of Cr in the steel increases, the A cm line of the steel shifts to the lower carbon side, which reduces the amount of saturated carbon in austenite and makes it easier to form carbides. On the other hand, Cr
In the case of a small amount of steel, even if carburizing is carried out in a carburizing atmosphere exceeding Acm, carbides will not form within the austenite grains, but will not form in a network or block form at the austenite grain boundaries. As mentioned above. However, as in the thermal cycle of the present invention, the product is first precarburized at a carbon potential of A cm or less of the steel to be treated so that the surface carbon content of the product is at least eutectoid, and then air cooled or quenched.
The temperature range from Ac 1 to the carbide generation treatment temperature is maintained at a heating rate of 20℃/20℃ on the surface of the product while maintaining a carbon potential that exceeds the Acm of the steel to be treated.
If carburizing is carried out for an appropriate time while maintaining a carbon potential exceeding A cm at the carbide generation treatment temperature, the volume ratio is 30 mm from the surface of the product to a depth of 0.1 to 0.4 mm. % or more of pseudospherical or spherical carbide can be obtained. The reason for this is as follows. For example, a case will be described in which the amount of surface carbon during preliminary carburization is made into a eutectoid composition.
When the product is air-cooled after preliminary carburizing, the near surface of the product has a bainite or pearlite structure. In the carbide generation process, when the Ac value near the surface of the product exceeds 1 point, bainite or pearlite transforms into austenite. Immediately after transformation, the amount of carbon in austenite is lower than in the eutectoid composition. Therefore, undissolved carbides exist in austenite. This undissolved carbide tends to dissolve into austenite with the passage of time or an increase in temperature. However, since the carbon potential of the atmosphere exceeds Acm, the unsaturated austenite near the surface quickly becomes saturated as carbon diffuses from the surface, so undissolved carbides remain without being dissolved in the austenite. However, since the amount of saturated carbon in austenite increases as the temperature rises, if the heating rate above the Ac point is too fast, unsaturated austenite will be saturated faster than the rate at which unsaturated austenite is saturated by carbon diffusion from the surface. The rate at which carbides dissolve into unsaturated austenite becomes faster, and all of the carbides dissolve into austenite. The upper limit of this heating rate is 20°C/min. In other words, if the temperature range from Ac 1 point to the carbide formation temperature is increased at a heating rate of 20°C/min or less while maintaining the carbon potential exceeding Acm, and maintained at the carbide formation temperature for an appropriate time. ,
The undissolved carbide grows to become pseudospherical or spherical carbide. If the martensitic structure is created by quenching after preliminary carburizing, the martensite will decompose during the process of heating up to the Ac 1 point and produce spheroidal carbides. Of these, those undissolved in austenite become nuclei, and according to the method of the present invention, mainly spherical carbides are produced. If the surface carbon content during preliminary carburization is a hyper-eutectoid composition, the amount of undissolved carbide immediately after austenitization at a temperature exceeding the Ac 1 point will be greater than when the surface carbon content during preliminary carburization is a eutectoid composition. many. Therefore, the amount of carbides after carbide generation treatment is greater than in the case of eutectoid composition. In addition, if the surface carbon content during preliminary carburizing has a hypereutectoid composition, thin network carbides will be formed at the austenite grain boundaries when air cooled, but these carbides will be fragmented during heating during the carbide generation process and become spherical. Become. If the surface carbon content during preliminary carburizing is hypoeutectoid, the volume fraction of carbide after carbide generation treatment will be less than 30%, so heat resistance, wear resistance, and pitting resistance will be lower than that of normal carburized products. and it doesn't improve much. Therefore, it is necessary that the amount of surface carbon during preliminary carburization be greater than that of eutectoid. Furthermore, if the carbon potential during preliminary carburizing exceeds Acm (the amount of surface carbon exceeds Acm), thick net-like or blocky carbides will be generated at the austenite grain boundaries, so the carbon potential during preliminary carburizing will exceed Acm. Must not be. Carbide generation treatment temperature is Ac 1 for low to medium carbon low alloy steel.
The lower limit is 750℃ just above the point, and from the viewpoint of the durability limit of the current carburizing furnace and the coarsening of crystal grains in the core, the lower limit is 950℃.
is the upper limit. Further, the upper limit of the carbon content of the steel to be subjected to the heat treatment method of the present invention is 0.5%. This is because when the carbon content of the steel exceeds 0.5%, the carbide layer becomes less than 0.05 mm, resulting in a decrease in heat resistance, wear resistance, and pitting resistance. Therefore, from a practical standpoint, the steel to be subjected to the heat treatment method of the present invention is low-medium carbon and low-alloy steel. Example Figure 2 shows carburized steel JIS SCM21 (0.18C, 0.21Si,
0.63Mn, 0.011P, 0.016S, 0.07Ni, 0.94Cr,
0.18Mo) and JIS SNCM21 (0.23C, 0.27Si,
0.76Mn, 0.014P, 0.018S, 0.45Ni, 0.53Cr,
0.20Mo) using propane modified RX gas 930
After precarburizing for 6 to 12 hours at 0.06 to 0.25% CO 2 (carbon potential 0.50 to 1.48%) in the temperature range of ~980℃, air cooling or quenching to Ac 1 to 900
Carbon potential exceeding Acm up to ℃ (for example, 1.0% CO 2 at 750℃, 0.61% CO 2 at 800℃,
The temperature was raised at a heating rate of 3°C/min while maintaining 0.25% CO 2 (at 850°C), followed by a 6-hour carbide generation treatment at 900°C and 0.12% CO 2 (carbon potential 1.85%), followed by oil cooling. This figure shows the relationship between the carbide volume fraction at a depth of 0.1 mm from the surface of the product and the surface carbon content during preliminary carburization.
The eutectoid carbon content of SCM21 and SNCM21 is approximately 0.78%
The Acm carbon content at the preliminary carburizing temperature (930°C) is 1.30%. When the volume fraction of carbide is less than 30%, heat resistance, wear resistance, and pitting resistance do not improve much compared to conventional carburizing methods.
If the lower limit of the carbide volume fraction is 30%, the lower limit of the surface carbon content during preliminary carburization will be close to the eutectoid composition. Furthermore, if the surface carbon content exceeds the A cm line of the steel to be treated, it is not preferable because network or block-like carbides are formed at the austenite grain boundaries. Therefore, the carbon potential during preliminary carburization to generate pseudospherical or spherical carbides is Acm greater than eutectoid.
The following is true. Figure 3 shows the same JIS composition as that used in Figure 2.
SCM21, SNCM21 carburized steel with 0.18~0.06% CO2 (carbon potential) in the temperature range of 930~980℃
After carburizing for 6 to 12 hours at 0.80 to 1.30%), air cooling.
The heating rate on the surface of the item was increased at various rates in the range of 0.12 to 30°C/min from Ac 1 to 900°C while maintaining a carbon potential exceeding Acm, and the temperature was increased to 900°C and 0.12% CO 2 (carbon potential
This figure shows the relationship between the volume fraction of carbide at a depth of 0.1 mm from the surface of an item subjected to carbide generation treatment for 6 hours at 1.85%) and the heating rate from Ac 1 to 900°C. For the above-mentioned reasons, if the lower limit of the carbide volume fraction is set to 30%, the upper limit of the heating rate will be around 20° C./min. Furthermore, from a practical standpoint, the lower limit of the heating rate would be around 0.3°C/min. Figure 4 shows that various steels with different carbon contents (chemical compositions are shown in the table) were carburized for 10 hours in RX gas of 0.13% CO 2 (carbon potential 1.07%) at a temperature of 930°C, and then cooled in air. The temperature was increased at a heating rate of 3°C/min from Ac 1 point to 850°C to 930°C while maintaining a carbon potential exceeding Acm, and in this temperature range 0.25 to 0.06% CO 2 (carbon potential
This figure shows the relationship between the thickness of the carbide layer and the carbon content of the material after carburizing for 6 hours in RX gas (1.63 to 2.10%) and cooling in oil. The carbon content of the material is 0.5
If the carbon content exceeds 0.05%, the thickness of the carbide layer will be less than 0.05mm, and the heat resistance, abrasion resistance, and pitting resistance will decrease, so the upper limit of the carbon content of the material will be around 0.5%.
The reason why the thickness of the carbide layer becomes thinner as the carbon content of the material increases is that the higher the carbon content of the material, the smaller the difference between the carbon potential of the carburizing atmosphere and the carbon content of the material, which slows down the diffusion rate of carbon in austenite. It is thought that this is because
【表】
第５図のＡ〜Ｄは前述した実施例のうちから、
４種の鋼について予備浸炭後および炭化物生成処
理後の炭素濃度分布を示したものである。図のよ
うにいずれの場合にも表面炭素量は２％を越えて
いる。図中の斜線部分は炭化物が生成している範
囲である。
第６図は第２図に用いたものと同一組成の
SCM21，SNCM21を、図中の条件にて処理した
ものの表面から0.1mmのかたさと焼もどし温度と
の関係を示したものである。
本発明の方法にて処理した鋼は従来の方法にて
処理した鋼よりも焼もどし軟化抵抗が著しく大き
い。
第７図は第４図に用いたものと同一組成の
SCM4，SNCM8を、図中の条件にて処理し、第
５図と同様の関係を示したものである。この場合
も本発明によるものは従来法によるものよりも焼
もどし軟化抵抗が著しく大きい。
第８図Ａ，Ｂ，ＣはSNCN21を本発明方法で浸
炭処理した場合の金属組織を400倍に拡大して示
す写真である。この各例ともそれぞれの予備浸炭
はカーボンポテンシヤルが1.1％、930℃で12時間
加熱し、その後空冷した。また各例の炭化物生成
処理は、第８図Ａに示すものは、カーボンポテン
シヤル1.3％、１℃／分で750℃に加熱して６時間
保持した後油冷した。第８図Ｂに示すものは、カ
ーボンポテンシヤル1.7％、１℃／分で850℃に加
熱して６時間保持した後油冷した。第８図Ｃに示
すものは、カーボンポテンシヤル20％、１℃／分
で950℃に加熱して６時間保持した後油冷した。
これらの写真でわかるように、表面から約0.1mm
までが体積率にて30％以上の擬球状炭化物とマル
テンサイトの混合組織であり、0.1mmより深部で
の炭化物は次第に減少するが、やはり擬球状炭化
物とマルテンサイトさらに少量の残留オーステナ
イトの混合組織が続く。なお炭化物の存在する深
さは鋼種によつて異なるが約0.3〜0.4mmである。
さらに第９図は第５図Ｂに示す例に用いた本発
明方法にて浸炭処理を施した鋼の表面からの深さ
mmに対する測定荷重500ｇのビツカース硬度を示
すもので、表面から深い範囲にわたつて高い硬度
となつた。なお深さ2.5mm付近ではＨv513であつ
た。
また第１０図は耐ピツチング性におよぼす炭化
物の体積率の影響を示す。なおこの場合の炭化物
の体積率は表面から0.05mm付近での測定値であ
る。また供試材の材質はSNCN23、SCM22を用い
た。さらに上記供試材の熱処理条件は、0.13％
CO2の雰囲気内で930℃で10時間加熱後空冷して
予備浸炭し、ついで730℃から850℃（0.25％
CO2）までＡcmを越えるカーボンポテンシヤルを
維持しつつ３℃／分の加熱速度で昇温し、そのま
ま６時間維持し、その後油冷し、180℃で３時間
保つた後空冷して炭化物生成処理をした。
耐ピツチングテストの条件は第１１図に示すよ
うに、直径26mmの供試材１に直径130mmの負荷ロ
ーラ２を潤滑状態で転接させる。そしてその面圧
は290Kg／mm2、すべり率は40％、供試材１の回転
数は1000rpm、潤滑油はエンジンオイル30番でそ
の流量は1.5／分、油温70℃である。
上記第１０図において、炭化物体積率が30％以
上になることにより耐ピツチング性が著しく向上
することがわかる。
なお第１０図における各点に付した数字は各点
で示されるそれぞれの供試材の表面から深さ0.1
mmまでの平均表面炭素量を示す。各供試材の平均
表面炭素量による耐ピツチング性を考察してみる
と、炭化物体積率が30％以上のものの平均表面炭
素量は2.0％以上であり、このことから、平均表
面炭素量が2.0％以上になると耐ピツチング性が
平均表面炭素量が0.7〜1.8％のものより著しく優
れた耐ピツチング性を有することがわかる。
本発明は以上のようになるから、炭素量が0.5
重量％以下の低中炭素合金鋼の表面付近に多量の
擬球状または球状の炭化物を生成させることがで
き、従来の浸炭品よりも耐熱性、耐摩耗性、特に
耐ピツチング性を著しく向上することができる。[Table] A to D in FIG. 5 are from the above-mentioned embodiments.
This figure shows the carbon concentration distributions of four types of steel after preliminary carburizing and after carbide generation treatment. As shown in the figure, the amount of surface carbon exceeds 2% in all cases. The shaded area in the figure is the area where carbide is generated. Figure 6 shows the same composition as that used in Figure 2.
This figure shows the relationship between hardness of 0.1 mm from the surface and tempering temperature for SCM21 and SNCM21 treated under the conditions shown in the figure. Steel treated with the method of the invention has significantly greater resistance to temper softening than steel treated with conventional methods. Figure 7 shows the same composition as that used in Figure 4.
SCM4 and SNCM8 are processed under the conditions shown in the figure, and the same relationships as in FIG. 5 are shown. In this case as well, the material according to the present invention has significantly greater resistance to temper softening than the material produced by the conventional method. FIGS. 8A, B, and C are photographs showing the metal structure of SNCN21 carburized by the method of the present invention, magnified 400 times. In each case, the preliminary carburization was performed at a carbon potential of 1.1%, heated at 930° C. for 12 hours, and then cooled in air. Regarding the carbide generation treatment of each example, the one shown in FIG. 8A was heated to 750° C. at a carbon potential of 1.3% at 1° C./min, held for 6 hours, and then cooled in oil. The one shown in FIG. 8B had a carbon potential of 1.7%, was heated to 850°C at 1°C/min, held for 6 hours, and then cooled in oil. The one shown in FIG. 8C was heated to 950° C. at a carbon potential of 20% at 1° C./min, held for 6 hours, and then cooled in oil.
As you can see in these photos, about 0.1mm from the surface
It is a mixed structure of pseudospherical carbide and martensite with a volume fraction of 30% or more, and although the carbide gradually decreases deeper than 0.1 mm, it is still a mixed structure of pseudospherical carbide, martensite, and a small amount of retained austenite. continues. The depth at which carbides exist varies depending on the type of steel, but is approximately 0.3 to 0.4 mm. Furthermore, Figure 9 shows the depth from the surface of the steel carburized by the method of the present invention used in the example shown in Figure 5B.
This shows the Vickers hardness at a measured load of 500 g per mm, and the hardness was high from the surface to a deep range. Furthermore, Hv was 513 at a depth of around 2.5mm. Moreover, FIG. 10 shows the influence of the volume fraction of carbide on pitting resistance. Note that the volume fraction of carbide in this case is a value measured at around 0.05 mm from the surface. The materials used for the test were SNCN23 and SCM22. Furthermore, the heat treatment conditions for the above sample material were 0.13%
After heating at 930℃ for 10 hours in a CO 2 atmosphere, precarburizing is performed by air cooling, and then from 730℃ to 850℃ (0.25%
The temperature was raised at a heating rate of 3°C/min while maintaining a carbon potential exceeding Acm up to CO 2 ), maintained at that temperature for 6 hours, then cooled with oil, kept at 180°C for 3 hours, and then air cooled for carbide generation treatment. Did. The conditions for the pitting resistance test are as shown in FIG. 11, in which a load roller 2 with a diameter of 130 mm is brought into contact with a test material 1 with a diameter of 26 mm in a lubricated state. The surface pressure was 290 Kg/mm 2 , the slip ratio was 40%, the rotational speed of test material 1 was 1000 rpm, the lubricating oil was engine oil No. 30, the flow rate was 1.5/min, and the oil temperature was 70°C. In FIG. 10 above, it can be seen that pitting resistance is significantly improved when the carbide volume fraction is 30% or more. Note that the numbers attached to each point in Figure 10 indicate the depth of 0.1 from the surface of the respective specimen material indicated by each point.
Shows the average surface carbon content up to mm. Considering the pitting resistance of each sample material based on the average surface carbon content, the average surface carbon content of those with a carbide volume fraction of 30% or more is 2.0% or more, which means that the average surface carbon content is 2.0% or more. It can be seen that when the average surface carbon content is 0.7 to 1.8%, the pitting resistance is significantly superior to that when the average surface carbon content is 0.7 to 1.8%. Since the present invention is as described above, the carbon content is 0.5
It is possible to generate a large amount of pseudospherical or spherical carbides near the surface of low-medium carbon alloy steel with a weight percentage of less than %, and the heat resistance, wear resistance, and especially pitting resistance are significantly improved compared to conventional carburized products. I can do it.
第１図は本発明一実施例の熱処理サイクルの説
明図、第２図は品物の表面から深さ0.1mmにおけ
る炭化物の体積率と予備浸炭時の表面炭素量との
関係を示す線図、第３図は品物の表面から深さ
0.1mmにおける炭化物の体積率と加熱速度との関
係を示す線図、第４図は炭化物層の厚さと素材の
炭素量との関係を示す線図、第５図のＡ，Ｂ，
Ｃ，Ｄは予備浸炭後および炭化物生成処理後の炭
素濃度分布を示す線図、第６図および第７図はそ
れぞれ焼もどし軟化抵抗の測定結果の説明図、第
８図Ａ，Ｂ，Ｃは本発明方法で浸炭処理した鋼の
組織を示す写真、第９図は表面からの深さに対す
る硬度を示す線図、第１０図は耐ピツチング性に
およぼす炭化物の体積率の影響を示すグラフ、第
１１図は試験装置を示す概略的説明図である。
Fig. 1 is an explanatory diagram of a heat treatment cycle according to an embodiment of the present invention, Fig. 2 is a diagram showing the relationship between the volume fraction of carbide at a depth of 0.1 mm from the surface of the article and the amount of surface carbon during preliminary carburization. Figure 3 shows the depth from the surface of the item.
A diagram showing the relationship between the carbide volume fraction and heating rate at 0.1 mm, Figure 4 is a diagram showing the relationship between the thickness of the carbide layer and the carbon content of the material, and Figure 5 A, B,
C and D are diagrams showing the carbon concentration distribution after preliminary carburizing and after carbide generation treatment, Figures 6 and 7 are explanatory diagrams of the measurement results of tempering softening resistance, respectively, and Figure 8 A, B, and C are diagrams showing the carbon concentration distribution after preliminary carburization and after carbide generation treatment. A photograph showing the structure of steel carburized by the method of the present invention, FIG. 9 is a diagram showing hardness versus depth from the surface, FIG. 10 is a graph showing the effect of carbide volume fraction on pitting resistance, and FIG. FIG. 11 is a schematic explanatory diagram showing the test device.
Claims (1)
以下のカーボンポテンシヤルにて表面炭素量が共
析以上となるように予備浸炭して冷却し、品物の
表面層をベイナイト、パーライトまたはマルテン
サイト組織としてから再び昇温して前記冷却にて
生じたベイナイトまたはパーライト中の炭化物を
核とするかまたは前記冷却にて生じたマルテンサ
イトを再加熱することによつて分解させ、粒状の
炭化物を発生させてこの炭化物を核とすることに
より、これらの核を消滅させないようにAc1点以
上の温度におけるカーボンポテンシヤルがＡcmを
越えるように維持しつつ、Ac1点から750〜950℃
の温度範囲まで20℃／分以下の加熱速度にて昇温
し、この温度範囲にてＡcmを越えるカーボンポテ
ンシヤルを維持しながら適当時間浸炭を行い、炭
化物の核を生成させて品物の表面から深さ0.4mm
までの範囲に体積率にて30％以上の擬球状または
球状の炭化物を生成させることを特徴とする鋼の
浸炭処理方法。 ２ 浸炭処理しようとする炭素量0.5％以下の低
中炭素低合金鋼のCr量を2.4％未満とした特許請
求の範囲第１項記載の鋼の浸炭処理方法。[Scope of Claims] 1. Low and medium carbon low alloy steel with a carbon content of 0.5% or less Acm
The product is pre-carburized and cooled so that the surface carbon content becomes eutectoid or higher at the following carbon potential, and the surface layer of the product is made into a bainite, pearlite, or martensite structure, and then the temperature is raised again to produce the bainite produced by the cooling. Alternatively, the carbides in pearlite can be used as nuclei, or the martensite produced by the cooling can be decomposed by reheating to generate granular carbides, and these carbides can be used as nuclei. 750 to 950℃ from Ac 1 point while maintaining the carbon potential at the temperature of Ac 1 point or more to exceed A cm so as not to disappear.
The temperature is raised at a heating rate of 20°C/min or less to a temperature range of 0.4mm
A method for carburizing steel, characterized by generating pseudospherical or spherical carbides with a volume fraction of 30% or more in a range of up to 30%. 2. The method for carburizing steel according to claim 1, wherein the Cr content of the low-medium carbon low alloy steel with a carbon content of 0.5% or less is less than 2.4%.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14218078A JPS5569252A (en) | 1978-11-20 | 1978-11-20 | Carburizing method for steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14218078A JPS5569252A (en) | 1978-11-20 | 1978-11-20 | Carburizing method for steel |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5569252A JPS5569252A (en) | 1980-05-24 |
| JPS6224499B2 true JPS6224499B2 (en) | 1987-05-28 |
Family
ID=15309223
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP14218078A Granted JPS5569252A (en) | 1978-11-20 | 1978-11-20 | Carburizing method for steel |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5569252A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006085549A1 (en) | 2005-02-08 | 2006-08-17 | Parker Netsushori Kogyo K.K. | High-concentration carburized/low-strain quenched member and process for producing the same |
| JP2010024535A (en) * | 2008-07-24 | 2010-02-04 | Aisin Seiki Co Ltd | Carburization method for steel |
| WO2019244504A1 (en) * | 2018-06-18 | 2019-12-26 | 株式会社小松製作所 | Method for producing machine components |
| WO2022154046A1 (en) | 2021-01-13 | 2022-07-21 | 日本精工株式会社 | Linear motion guide device |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH07828B2 (en) * | 1984-10-26 | 1995-01-11 | 大同特殊鋼株式会社 | Carburized parts |
| JP2773523B2 (en) * | 1992-03-19 | 1998-07-09 | 住友金属工業株式会社 | Heat treatment method for steel |
| JP4971751B2 (en) * | 2006-11-06 | 2012-07-11 | 本田技研工業株式会社 | Manufacturing method of high-concentration carburized steel |
| CN111549314A (en) * | 2020-05-21 | 2020-08-18 | 湖南特科能热处理有限公司 | Carburizing process for low-carbon steel thin-wall part |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5541908A (en) * | 1978-09-14 | 1980-03-25 | Hinode Kinzoku Netsuren Kk | Surface hardening method of steel |
-
1978
- 1978-11-20 JP JP14218078A patent/JPS5569252A/en active Granted
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5541908A (en) * | 1978-09-14 | 1980-03-25 | Hinode Kinzoku Netsuren Kk | Surface hardening method of steel |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006085549A1 (en) | 2005-02-08 | 2006-08-17 | Parker Netsushori Kogyo K.K. | High-concentration carburized/low-strain quenched member and process for producing the same |
| JPWO2006085549A1 (en) * | 2005-02-08 | 2008-06-26 | パーカー熱処理工業株式会社 | High concentration carburizing / low strain quenching member and method of manufacturing the same |
| JP4627776B2 (en) * | 2005-02-08 | 2011-02-09 | パーカー熱処理工業株式会社 | High concentration carburizing / low strain quenching member and method of manufacturing the same |
| JP2010024535A (en) * | 2008-07-24 | 2010-02-04 | Aisin Seiki Co Ltd | Carburization method for steel |
| WO2019244504A1 (en) * | 2018-06-18 | 2019-12-26 | 株式会社小松製作所 | Method for producing machine components |
| JP2019218583A (en) * | 2018-06-18 | 2019-12-26 | 株式会社小松製作所 | Manufacturing method of mechanical component |
| US11326220B2 (en) | 2018-06-18 | 2022-05-10 | Komatsu Ltd. | Method for producing machine component |
| WO2022154046A1 (en) | 2021-01-13 | 2022-07-21 | 日本精工株式会社 | Linear motion guide device |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5569252A (en) | 1980-05-24 |
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