JPH0213004B2 - - Google Patents
Info
- Publication number
- JPH0213004B2 JPH0213004B2 JP56153924A JP15392481A JPH0213004B2 JP H0213004 B2 JPH0213004 B2 JP H0213004B2 JP 56153924 A JP56153924 A JP 56153924A JP 15392481 A JP15392481 A JP 15392481A JP H0213004 B2 JPH0213004 B2 JP H0213004B2
- Authority
- JP
- Japan
- Prior art keywords
- rolling
- temperature range
- cooling
- reduction
- less
- 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 - Lifetime
Links
- 238000005096 rolling process Methods 0.000 claims description 68
- 229910001566 austenite Inorganic materials 0.000 claims description 33
- 238000001816 cooling Methods 0.000 claims description 31
- 229910000831 Steel Inorganic materials 0.000 claims description 17
- 239000010959 steel Substances 0.000 claims description 17
- 229910000859 α-Fe Inorganic materials 0.000 claims description 16
- 229910001562 pearlite Inorganic materials 0.000 claims description 11
- 238000000034 method Methods 0.000 claims description 7
- 229910000746 Structural steel Inorganic materials 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 230000000694 effects Effects 0.000 description 12
- 239000000203 mixture Substances 0.000 description 12
- 238000001953 recrystallisation Methods 0.000 description 11
- 229910001563 bainite Inorganic materials 0.000 description 8
- 238000010438 heat treatment Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- 230000009466 transformation Effects 0.000 description 7
- 230000007423 decrease Effects 0.000 description 6
- 238000000137 annealing Methods 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 238000007796 conventional method Methods 0.000 description 4
- 238000005520 cutting process Methods 0.000 description 4
- 238000005098 hot rolling Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 229910000851 Alloy steel Inorganic materials 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000012669 compression test Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000001771 impaired effect Effects 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 1
- 238000010273 cold forging Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 230000001050 lubricating effect Effects 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- LRXTYHSAJDENHV-UHFFFAOYSA-H zinc phosphate Chemical compound [Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O LRXTYHSAJDENHV-UHFFFAOYSA-H 0.000 description 1
- 229910000165 zinc phosphate Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
Description
本発明は、構造用鋼線・棒鋼の直接軟化熱処理
方法に関するものである。
一般に、自動車用ギヤ、ボルト、シヤフトなど
に用いられる構造用合金鋼鋼線及び棒鋼は熱間圧
延材に軟化焼鈍処理を施した後、加工される。こ
れは熱間圧延材の硬度が極めて高く、そのまま切
削加工や冷間鍛造等を行うと工具寿命の低下、切
削能率の低下、割れの発生などが起こるためであ
る。このため、例えばSCM435では760℃２時間
保持後、650℃まで15℃／時の徐冷といつた熱処
理が行なわれる。
したがつてこの処理のため加熱用熱源等の設備
が必要なだけでなく、スケール付着への対策など
省資源、省エネルギー、コスト、生産性など多く
のロスがある。
本発明は、冷間鍛造性及び切削性に優れた鋼
線・棒鋼の製造に際し、熱間圧延材に軟化焼鈍処
理を施した後に加工する従来の製造方法の有する
前記諸欠点を除去、改善して、従来方法による如
き軟化焼鈍を行なわずに、直接熱間圧延により冷
間鍛造性及び切削性に優れる構造用鋼線・棒鋼を
製造するための直接軟化熱処理方法を提供するこ
とを目的とするものであり、特許請求の範囲記載
の方法を提供することによつて前記目的を達成す
ることができる。すなわち本発明は、
C0.25超〜0.50wt％、（以下単に「％」で略記す
る）、Si0.10〜0.50％、Mn0.3〜1.8％を含み、か
つCr0.2〜1.5％、Mo0.1〜0.8％およびNi0.3〜1.5
％のうちから選ばれる１種または２種以上を含有
し、残部がFeおよび不可避的不純物からなる鋼
に対し、1000℃〜1250℃の温度範囲で30〜80％の
圧下率で圧延するオーステナイト粒微細化のため
の第１段圧延と、これに続く750〜1000℃未満の
温度範囲へ冷却し、該温度範囲内で50〜80％の圧
下率で圧延することによる、オーステナイト粒に
歪を付与するための第２段圧延とを施し、その後
１℃／秒以下の冷却速度で冷却することにより、
フエライトパーライト組織とすることを特徴とす
る構造用鋼線・棒鋼の直接軟化処理方法に関する
ものである。
次に本発明を詳細に説明する。
本発明において成分組成を限定する理由を説明
する。
Ｃは鋼の焼入性を向上させ、強度を容易に上昇
させるに有効な元素であるが、Ｃは0.25％以下で
は上記効果が得られず、一方Ｃは0.50％より多い
と焼入性が高まり過ぎて被削性が悪化して本発明
の目的を達成することができないので、Ｃは0.25
超〜0.50％の範囲内にする必要がある。
Siは脱酸を促進し、強度を上昇させる点で、Ｃ
と同様に有効な元素であるが、Siは0.10％より少
ないと前記効果が少なく、一方0.50％より多いと
硬化が著しく、冷間鍛造性ならびに切削性を損う
ので、Siは0.10〜0.50％の範囲内にする必要があ
る。
Mnは焼入性を向上させ、強度を上昇させる作
用のある元素であるが0.3％より少ないと前記作
用が少なく、一方1.8％より多いと焼入性が高く
なり過ぎると共に硬化が著しく、冷間鍛造性なら
びに切削性を損うので、Mnは0.3〜1.8％の範囲
内にする必要がある。
本発明によれば、Ｃ、Si、Mnと共に必要に応
じてCr、Mo、Niのうちから選ばれる何れか１種
または２種以上をCrにあつては0.2〜1.5％、Mo
にあつては0.1〜0.8％、Niにあつては0.3〜1.5％
を含有させることができる。
Crは固溶強化元素として知られ、また焼入性
を向上させて強度を上昇させる作用を有する元素
であるが、Crは0.2％より少ないと前記作用が少
なく、一方1.5％より多いと焼入性が高くなり過
ぎ、また多量の添加はコストを上昇させるばかり
でなく切削性、冷間鍛造性及び燐酸亜鉛等の潤滑
被膜の付着性を低下させるので、Crは0.2〜1.5％
の範囲内にすることが有利である。
Moは強い固溶強化性を有し、焼入性を向上さ
せ、かつ小量の含有は切削性を向上させる作用を
有する元素であるが、Moは0.10％より少ないと
前記作用が期待できず、一方0.8％より多いと硬
化が著しく高くなり、焼入性が上昇し、冷間鍛造
性および切削性を損うのでMoは0.1〜0.8％の範
囲内にすることが有利である。
Niは鋼の延性を向上させると共に、焼入性を
向上させるに有効な元素であるが、0.3％より少
ないと上記効果が少なく、一方1.5％より多いと
Niが高価な元素であるためコストが上昇すると
共に焼入性が高くなり過ぎて本発明の目的を達成
することができなくなるので、Niは0.3〜1.5％の
範囲内にすることが有利である。
本発明によれば、上記成分組成の鋼を、通常の
ビレツトとし、そしてオーステナイト粒の再結晶
温度範囲の1000〜1250℃の温度領域において圧下
率が30〜80％の範囲で繰返し第１段の圧延を施
す。この第１段階の、いわゆるオーステナイト微
細化のための第１段階の圧延により、再結晶して
オーステナイトのより微細化が達成される。この
第１段階の圧延後は、さらに、オーステナイト粒
の未再結晶温度範囲へ冷却して750〜1000℃の温
度範囲内での第２段階の圧延ならびに冷却を経て
冷間加工性に優れたフエライト・パーライト組織
を容易に形成させることができる。
一般に鋼の化学組成や圧延後の冷却条件が固定
された場合には、製品である鋼線・棒鋼等のミク
ロ組織の性状は主としてオーステナイト粒径に依
存し、オーステナイト粒径が大きい場合にはその
粒径が大きいほど焼入性は上昇し、マルテンサイ
トおよびベイナイトが形成され易くなり、一方オ
ーステナイト粒径が小さい場合にはフエライトお
よびパーライト組織が形成され易くなることが知
られている。
また圧延工程においてオーステナイト粒の平均
粒径が微細になつても粗大オーステナイト粒が混
在している時には、変態後においてフエライト−
パーライト粒間に粗大なベイナイトなどの組織が
存在することになつて切削性及び冷間鍛造性が低
下することが知られている。
かかる組成の生成による切削性及び冷間鍛造性
の低下を避けるため、本発明によれば鋼を少なく
とも1000℃以上1250℃以下（加熱温度以下）の範
囲内で30〜80％の範囲内の圧下率の圧延をする必
要がある。この圧下率が30％未満では再結晶によ
るオーステナイト粒の微細化が達成できず、また
80％を超える圧下率圧延では効果が飽和する。
しかしながら、このように圧延してもオーステ
ナイト粒の微細化は未だ十分には達成されないの
で、本発明によれば前記第１段の圧延に引続い
て、オーステナイト粒の未再結晶温度範囲内であ
る750〜1000℃未満の温度範囲内で50％〜80％以
下の圧下率で圧延する必要がある。このような圧
延を行う理由は、第１図に示すように、1000℃未
満で行う圧延が圧下率０％では、たとえば1000℃
以上での圧延において80％以上の圧下を加えたと
しても硬さの低下が不十分となる。一方、第２図
に示すように、この段階での圧延圧下率は80％を
超えると効果が飽和する。以上説明したように、
このような圧延を行うことによつて、オーステナ
イト粒は再結晶を生起することなく圧下率に応じ
て伸長する。すなわち圧延による加工歪はオース
テナイト粒界や粒内に変形帯などの形ですべて蓄
積されるので、オーステナイトの安定度は急激に
低下し、フエライト変態が促進される。
本発明によれば、後述する如く１℃／秒以下の
冷却速度のもとで冷却されることにより、析出し
たフエライト粒は十分に粒成長することができ
る。この際フエライト粒の発生個所はオーステナ
イト粒界ばかりでなく粒内にも多数発生するため
均一性が向上し、この時未変態オーステナイトも
１℃／秒以下の冷却速度のもとでの冷却により均
一なパーライト組織となる。従つて通常熱間圧延
材に見られるベイナイト組織の混入が防止され、
この結果、本発明によれば鋼は著しく軟化して冷
間鍛造性及び切削性が著しく向上するのである。
次に各温度領域において圧下率を限定した理由
を実験データに基いて説明する。
The present invention relates to a direct softening heat treatment method for structural steel wires and bars. Generally, structural alloy steel wires and steel bars used for automobile gears, bolts, shafts, etc. are processed after being subjected to a softening annealing treatment on hot rolled materials. This is because hot-rolled materials have extremely high hardness, and if they are subjected to cutting, cold forging, etc. as they are, tool life will be reduced, cutting efficiency will be reduced, and cracks will occur. For this reason, for example, in SCM435, heat treatment is performed such as holding at 760°C for 2 hours and then slowly cooling to 650°C at 15°C/hour. Therefore, this process not only requires equipment such as a heat source for heating, but also involves many losses in terms of resource and energy conservation, cost, productivity, etc., such as countermeasures against scale adhesion. The present invention eliminates and improves the various drawbacks of the conventional manufacturing method in which hot-rolled materials are subjected to softening annealing treatment and then processed when manufacturing steel wires and bars with excellent cold forgeability and machinability. It is an object of the present invention to provide a direct softening heat treatment method for producing structural steel wires and bars with excellent cold forgeability and machinability by direct hot rolling without performing softening annealing as in conventional methods. The above object can be achieved by providing the method described in the claims. That is, the present invention contains more than 0.25 to 0.50 wt% of C (hereinafter simply abbreviated as "%"), 0.10 to 0.50% of Si, 0.3 to 1.8% of Mn, and 0.2 to 1.5% of Cr, Mo0 .1~0.8% and Ni0.3~1.5
Austenite grains that are rolled at a reduction rate of 30 to 80% in a temperature range of 1000°C to 1250°C for steel containing one or more selected from % and the remainder consisting of Fe and unavoidable impurities. First stage rolling for refinement, followed by cooling to a temperature range of 750 to less than 1000℃, and applying strain to austenite grains by rolling at a reduction rate of 50 to 80% within this temperature range. By performing a second stage rolling to achieve
The present invention relates to a method for directly softening structural steel wires and bars, which are characterized by having a ferrite-pearlite structure. Next, the present invention will be explained in detail. The reason for limiting the component composition in the present invention will be explained. C is an effective element for improving the hardenability of steel and easily increasing its strength, but if C is less than 0.25%, the above effects cannot be obtained, while if it is more than 0.50%, the hardenability is reduced. C is 0.25 because if it is too high, the machinability will deteriorate and the purpose of the present invention cannot be achieved.
Must be within the range of ultra~0.50%. Si promotes deoxidation and increases strength, and C
However, if Si is less than 0.10%, the above effect will be small, while if it is more than 0.50%, hardening will be significant and cold forgeability and machinability will be impaired. Must be within the range. Mn is an element that has the effect of improving hardenability and increasing strength, but if it is less than 0.3%, this effect will be small, while if it is more than 1.8%, the hardenability will be too high and hardening will be significant, resulting in cold Since Mn impairs forgeability and machinability, it is necessary to keep it within the range of 0.3 to 1.8%. According to the present invention, in addition to C, Si, and Mn, any one or more selected from Cr, Mo, and Ni may be added in an amount of 0.2 to 1.5% in the case of Cr, and Mo in an amount of 0.2 to 1.5%.
0.1-0.8% for Ni, 0.3-1.5% for Ni
can be contained. Cr is known as a solid solution strengthening element and has the effect of improving hardenability and increasing strength; however, if Cr is less than 0.2%, this effect will be small, while if it is more than 1.5%, it will not harden. Cr content is 0.2 to 1.5%, as adding too much will not only increase cost but also reduce machinability, cold forgeability, and adhesion of lubricating films such as zinc phosphate.
It is advantageous to keep it within the range of . Mo is an element that has strong solid solution strengthening properties, improves hardenability, and has the effect of improving machinability when contained in small amounts, but if Mo is less than 0.10%, the above effect cannot be expected. On the other hand, if Mo is more than 0.8%, hardening becomes extremely high, hardenability increases, and cold forgeability and machinability are impaired, so it is advantageous to keep Mo in the range of 0.1 to 0.8%. Ni is an effective element for improving the ductility and hardenability of steel, but if it is less than 0.3%, the above effects will be small, while if it is more than 1.5%, the above effect will be small.
Since Ni is an expensive element, the cost increases and the hardenability becomes too high, making it impossible to achieve the purpose of the present invention, so it is advantageous to keep Ni in the range of 0.3 to 1.5%. . According to the present invention, the steel having the above-mentioned composition is made into a normal billet, and the first stage is repeatedly rolled at a rolling reduction of 30 to 80% in the temperature range of 1000 to 1250°C, which is the recrystallization temperature range of austenite grains. Apply rolling. This first stage of rolling for so-called austenite refinement achieves further refinement of austenite through recrystallization. After this first stage of rolling, the austenite grains are further cooled to a non-recrystallized temperature range, and then subjected to a second stage of rolling and cooling within a temperature range of 750 to 1000°C to form a ferrite with excellent cold workability. - A pearlite structure can be easily formed. Generally, when the chemical composition of steel and the cooling conditions after rolling are fixed, the microstructure properties of products such as steel wires and bars mainly depend on the austenite grain size, and if the austenite grain size is large, the It is known that the larger the grain size, the higher the hardenability and the easier formation of martensite and bainite, while the smaller the austenite grain size, the easier the formation of ferrite and pearlite structures. In addition, even if the average grain size of austenite grains becomes fine in the rolling process, if coarse austenite grains are mixed, ferrite-
It is known that the presence of coarse structures such as bainite between pearlite grains reduces machinability and cold forgeability. In order to avoid deterioration of machinability and cold forgeability due to the formation of such a composition, according to the present invention, steel is reduced within a range of 30 to 80% at a temperature of at least 1000°C to 1250°C (below the heating temperature). It is necessary to do some rolling. If this reduction rate is less than 30%, refinement of austenite grains by recrystallization cannot be achieved, and
The effect is saturated when the rolling reduction exceeds 80%. However, even with such rolling, the austenite grains are still not sufficiently refined, so according to the present invention, following the first stage rolling, the temperature is within the non-recrystallization temperature range of the austenite grains. It is necessary to roll at a reduction rate of 50% to 80% or less within a temperature range of 750 to less than 1000°C. The reason for performing such rolling is that, as shown in Figure 1, if rolling is performed at a temperature below 1000°C and the rolling reduction is 0%, for example, 1000°C
Even if a reduction of 80% or more is applied in the above rolling process, the reduction in hardness will be insufficient. On the other hand, as shown in FIG. 2, the effect is saturated when the rolling reduction ratio at this stage exceeds 80%. As explained above,
By performing such rolling, the austenite grains are elongated according to the rolling reduction ratio without causing recrystallization. In other words, all the working strain caused by rolling is accumulated in the form of deformation bands at austenite grain boundaries and inside grains, so the stability of austenite decreases rapidly and ferrite transformation is promoted. According to the present invention, the precipitated ferrite grains can be sufficiently grown by cooling at a cooling rate of 1° C./second or less as described later. At this time, many ferrite grains are generated not only at the austenite grain boundaries but also within the grains, improving uniformity. It becomes a pearlite structure. Therefore, the inclusion of bainite structure, which is normally found in hot rolled materials, is prevented.
As a result, according to the present invention, the steel is significantly softened and its cold forgeability and machinability are significantly improved. Next, the reason for limiting the rolling reduction rate in each temperature range will be explained based on experimental data.
【表】
上記第１表に示す成分組成のビレツトを1200℃
まで加熱した後、1000℃以上の温度範囲内で圧下
率を種々変化させてそれぞれ圧延してから0.5
℃／秒の冷却速度で冷却した場合と、同様に1200
℃まで加熱後1000℃以上の温度範囲内で圧下率を
種々変化させて圧延後、さらに750〜1000℃未満
の温度域において再び50％の圧下率で圧延した
後、0.5℃／秒の冷却速度で冷却した場合との２
つの場合について硬さをそれぞれ測定した。第１
図はこの結果を1000℃以上の温度領域での圧下率
と硬さとの関係において示す図である。同図から
明らかなように1000℃未満で50％圧下率の圧延を
施した本発明による場合は1000℃以上の温度領域
における圧下率が30％以上になると硬さが著しく
低下して軟化し、80％付近で飽和することが判
る。
一方前者の1000℃以下の温度領域において全然
圧延を施さない場合は硬さは高く、圧下率が増加
しても硬さの低下の程度は低くて軟化は進行する
ことが困難であるので冷間鍛造及び切削加工は困
難であることが判る。
前記実験データより判るように、本発明によれ
ば、オーステナイト粒を微細化することができ、
しかも熱間圧延を施すことによるだけで軟化する
ことができる。かかる軟化が達成される理由は、
圧下率が30％以上になるまで繰返し圧下すると、
ビレツトの加熱によつて粗大化したオーステナイ
ト粒は再結晶を起して細粒化するからである。
本発明によれば、1000℃以上の温度領域におい
て圧下率30％以上になるまで圧延することによつ
て、オーステナイト粒径は約40μｍ程度まで再結
晶により細粒化されるが、この状態から冷却して
変態させても組織の大半をフエライト−パーライ
トにすることは難しく、マルテンサイトおよびま
たはベイナイトの混入は避け難い。すなわち従来
方法によれば1000℃以上で圧延を施して充分にオ
ーステナイトを微細化した後、上記温度から放冷
乃至徐冷されるので、組織の軟化は十分には達成
されないのである。
本発明者等は、完全なフエライト−パーライト
組織を得るには上記細粒化されたオーステナイト
粒に対して、さらにより多くのフエライト発生核
を与えてフエライト−パーライトへの変態を誘引
することに想到したのである。すなわちオーステ
ナイト粒の未再結晶温度範囲における圧延によれ
ばオーステナイト粒は再結晶を起こさず伸長され
る。従つてオーステナイト粒未再結晶温度範囲で
ある750〜1000℃未満の温度範囲内で圧延すると
オーステナイト粒界には加工歪が蓄積され、オー
ステナイト粒内には変形帯および転位が数多く導
入される。かかる変形帯および転位の増加によつ
てオーステナイトの安定性は減少し、フエライト
変態が促進されるのに至るものと本発明者らは考
えた。
よつて本発明者らは、第１表に示す成分組成の
ビレツトについて1200℃に加熱してから、1000℃
以上の温度域で30％の圧下率で圧延を行つて、そ
の後750〜1000℃未満の温度域で圧下率を変化さ
せて圧延し、0.5℃／秒で冷却した場合と、同一
成分組成のビレツトを1200℃に加熱してから、そ
の後1000℃以上の温度域で圧延することなく750
〜1000℃未満の温度域で圧下率を変化させて圧延
し、0.5℃／秒で冷却した場合とについて750〜
1000℃未満の温度域での圧下率と硬さとの関係を
調べ、この関係を第２図に示す。
すなわち、第２図から明らかなとおり、本発明
によるごとく、1000℃以上の温度域において圧下
率30％まで圧延し、その後750〜1000℃未満の温
度領域で圧延した場合は、1000℃以上の温度域で
圧延しない場合に比べて、硬さレベルが著しく低
下し、軟化している。また、本発明により圧延し
た場合は、圧下率が50％以上になると硬さが著し
く低下し、軟化するのに対し、圧下率が50％未満
では硬さの低下率は小さい。また、更に1000℃以
上の温度域での圧延を行なわなかつた場合は、
750〜1000℃の温度領域において圧延を強化し、
圧下率が65％以上となると硬さは急激に低下する
が、元来がそのレベルが高いため、低下したと云
つてもその絶対値は高い。
次に圧延温度を750〜1000℃の範囲内に限定す
る理由を説明する。
本発明によれば、成分組成上Ar3変態点は700
℃付近であるため、750℃より低い温度で圧延を
施すと析出したフエライト粒を加工することにな
つて材質を劣化させるので750℃以上で圧延を施
す必要がある。
以上の通りに、圧延を２段階に分け、つまり
1000℃以上1250℃以下のオーステナイト粒再結晶
温度域においては圧下率が30％以上80％以下の範
囲に達するまで圧延し、その後、750℃以上1000
℃未満のオーステナイト粒未再結晶温度域におい
ては圧下率が50％以上80％以下になるように圧延
し、このように圧延された鋼を１℃／秒以下の冷
却速度で変態終了まで冷却する。この様に冷却す
ると、フエライト粒が十分に発生及び成長し、ほ
とんどマルテンサイトまたはベイナイトの発生は
抑えられ、十分軟化したフエライト−パーライト
組織が得られる。この場合、冷却速度を１℃／秒
以下と限定した理由は、本発明の化学組成及び圧
延条件の範囲では１℃／秒を越えるとフエライト
粒の発生及び成長が不完全となるとともに、冷間
鍛造性及び切削性を劣化させるマルテンサイトま
たはベイナイトの混入が起り、軟化が不完全とな
るからである。
次に本発明を実施例について比較例と比較して
説明する。
実施例 １
第１表に示す成分組成の鋼ビレツトを第２表に
示す圧延条件ならびに冷却速度条件によつて製造
した。[Table] A billet with the composition shown in Table 1 above was heated to 1200℃.
After heating to 0.5℃, the rolling reduction was varied within a temperature range of 1000℃ or higher, and then rolled to 0.5℃.
1200 °C, similar to when cooling at a cooling rate of °C/sec.
After heating to 1000°C, rolling with various reduction rates within a temperature range of 1000°C or higher, and then rolling again at a 50% reduction in a temperature range of 750 to less than 1000°C, followed by cooling at a cooling rate of 0.5°C/sec. 2 with the case of cooling with
The hardness was measured in each case. 1st
The figure shows this result in terms of the relationship between rolling reduction and hardness in a temperature range of 1000°C or higher. As is clear from the figure, in the case of the present invention in which rolling is performed at a reduction rate of 50% at a temperature below 1000°C, when the reduction rate becomes 30% or more in a temperature range of 1000°C or higher, the hardness decreases significantly and becomes soft. It can be seen that it is saturated around 80%. On the other hand, if no rolling is performed at all in the former temperature range of 1000℃ or less, the hardness will be high, and even if the rolling reduction rate increases, the degree of decrease in hardness will be low and it will be difficult for softening to proceed. Forging and machining prove difficult. As can be seen from the above experimental data, according to the present invention, austenite grains can be refined,
Moreover, it can be softened simply by hot rolling. The reason why such softening is achieved is that
If the reduction is repeated until the reduction rate is 30% or more,
This is because austenite grains that have become coarse due to heating of the billet undergo recrystallization and become finer grains. According to the present invention, by rolling to a reduction rate of 30% or more in a temperature range of 1000°C or higher, the austenite grain size is refined by recrystallization to about 40 μm. From this state, cooling Even if the structure is transformed into ferrite-pearlite, it is difficult to make the majority of the structure into ferrite-pearlite, and it is difficult to avoid the inclusion of martensite and/or bainite. That is, according to the conventional method, the austenite is sufficiently refined by rolling at 1000° C. or higher, and then allowed to cool or slowly cooled from the above temperature, so that sufficient softening of the structure is not achieved. The present inventors have come up with the idea that in order to obtain a complete ferrite-pearlite structure, more ferrite generation nuclei are provided to the fine-grained austenite grains to induce transformation into ferrite-pearlite. That's what I did. That is, by rolling in a temperature range in which austenite grains are not recrystallized, austenite grains are elongated without recrystallization. Therefore, if rolling is carried out within a temperature range below 750 to 1000°C, which is the non-recrystallization temperature range of austenite grains, processing strain will be accumulated at the austenite grain boundaries, and many deformation bands and dislocations will be introduced into the austenite grains. The present inventors thought that such an increase in deformation bands and dislocations decreases the stability of austenite and promotes ferrite transformation. Therefore, the present inventors heated a billet having the composition shown in Table 1 to 1200°C, and then heated it to 1000°C.
A billet with the same component composition is rolled at a rolling reduction rate of 30% in the above temperature range, then rolled at a temperature range of 750 to less than 1000°C with varying reduction rates, and cooled at a rate of 0.5°C/sec. Heated to 1200℃, then rolled to 750℃ without rolling in a temperature range of 1000℃ or higher.
~ 750 ~ for the case of rolling with varying reduction rates in the temperature range below 1000℃ and cooling at 0.5℃/sec
The relationship between rolling reduction and hardness in a temperature range below 1000°C was investigated, and this relationship is shown in Figure 2. That is, as is clear from Fig. 2, as in the present invention, when rolling is performed to a reduction rate of 30% in a temperature range of 1000°C or higher, and then rolled in a temperature range of 750 to less than 1000°C, the temperature of 1000°C or higher is The hardness level is significantly reduced and softened compared to the case where it is not rolled. Further, when rolling according to the present invention, when the rolling reduction is 50% or more, the hardness decreases significantly and softens, whereas when the rolling reduction is less than 50%, the reduction in hardness is small. In addition, if rolling is not performed in a temperature range of 1000℃ or higher,
Strengthen rolling in the temperature range of 750-1000℃,
When the rolling reduction rate is 65% or more, the hardness decreases rapidly, but since the level is originally high, even though it is said to have decreased, the absolute value is high. Next, the reason why the rolling temperature is limited to a range of 750 to 1000°C will be explained. According to the present invention, the Ar 3 transformation point is 700 due to the component composition.
Since the temperature is around 750°C, rolling at a temperature lower than 750°C will process precipitated ferrite grains and deteriorate the material, so it is necessary to perform rolling at a temperature of 750°C or higher. As mentioned above, rolling is divided into two stages, that is,
In the austenite grain recrystallization temperature range of 1000°C or higher and 1250°C or lower, rolling is performed until the rolling reduction reaches a range of 30% or higher and 80% or lower, and then rolled at 750°C or higher and 1000°C or higher.
In the austenite grain non-recrystallization temperature range below ℃, rolling is performed so that the rolling reduction is 50% or more and 80% or less, and the thus rolled steel is cooled at a cooling rate of 1℃/second or less until the transformation is completed. . By cooling in this manner, ferrite grains are sufficiently generated and grown, the generation of martensite or bainite is almost suppressed, and a sufficiently softened ferrite-pearlite structure is obtained. In this case, the reason why the cooling rate is limited to 1°C/sec or less is that within the range of the chemical composition and rolling conditions of the present invention, if the cooling rate exceeds 1°C/sec, the generation and growth of ferrite grains will be incomplete, and the cold This is because martensite or bainite, which deteriorates forgeability and machinability, occurs, resulting in incomplete softening. Next, the present invention will be explained by comparing examples with comparative examples. Example 1 A steel billet having the composition shown in Table 1 was manufactured under the rolling conditions and cooling rate conditions shown in Table 2.
【表】【table】
【表】
上記ビレツトの仕上寸法は16mmφである。この
時の硬さ、圧縮試験における限界据込率及び切削
における工具寿命を求めたところ、第２表に示す
通りであつた。なお切削性試験は、工具Ｐ−10ス
ロー アウエイタイプ、切削速度250m/min、切
込み2.0mm、送り速度0.24mm/Rev、無潤滑、VB＝
0.2mmFlankなる条件にて行つた。
第２表において、比較例のNo.１およびNo.２では
その冷却速度が１℃／秒以上であつて、この時は
フエライト組織中にベイナイトが多量に混入し、
硬さが高く、限界据込率及び工具寿命も低い。こ
れに対して、本発明による如く冷却速度が１℃／
秒以下である場合は、実施例No.３及びNo.４に示す
様に、硬さは著しく低下し、軟化しており限界据
込率及び工具寿命も著しく向上する。比較例No.５
は本発明の圧延条件範囲内で圧延したが、仕上温
度を700℃と低くした場合である。この場合はフ
エライト変態が一部始まり、それが加工を受ける
ため異方性が大きくなつて限界据込率及び工具寿
命が低下した。
比較例のNo.６は1000℃以上の温度域においての
み圧延を行い、適正冷却条件で冷却した場合であ
つて通常圧延に相当する。この場合はフエライト
の析出が不十分で、ベイナイト組織が大半を占め
る。これは750〜1000℃未満の温度域での圧延が
ないためフエライト変態が促進されないことによ
るものである。この結果硬さも高く、限界据込率
及び工具寿命は低い。
比較例No.７は750〜1000℃未満の温度域での圧
下率が30％と少ない場合である。この場合はNo.６
と同様にフエライトの発生が少なく、硬さが高
い。したがつて軟化不足のため限界据込率及び工
具寿命が低い。
なお、この実施例において採用した冷却法は、
電気ヒーターと冷却フアンとを具えたセラミツク
ス製フアイバーが内張りされた冷却室を通過させ
る方法である。
以上の様に圧延条件及び冷却条件が本発明によ
るそれらの限定外になると硬さが高くなり、限界
据込率及び工具寿命が低いのに対し、限定内であ
れば、熱間圧延のままで良好な冷間鍛造性及び切
削性を有する鋼を製造できた。
実施例 ２[Table] The finished dimension of the billet above is 16mmφ. At this time, the hardness, critical upsetting rate in the compression test, and tool life in cutting were determined and were as shown in Table 2. The machinability test was conducted using tool P-10 slow-away type, cutting speed 250 m/min, depth of cut 2.0 mm, feed rate 0.24 mm/Rev, no lubrication, V B =
It was conducted under the condition of 0.2mmFlank. In Table 2, in Comparative Examples No. 1 and No. 2, the cooling rate was 1°C/second or more, and in this case, a large amount of bainite was mixed into the ferrite structure.
It has high hardness, low upsetting rate and low tool life. On the other hand, according to the present invention, the cooling rate is 1°C/
If it is less than 2 seconds, as shown in Examples No. 3 and No. 4, the hardness is significantly reduced and softened, and the maximum upsetting rate and tool life are also significantly improved. Comparative example No.5
This is the case where rolling was carried out within the rolling condition range of the present invention, but the finishing temperature was lowered to 700°C. In this case, ferrite transformation started partially, and as it was processed, anisotropy increased and the critical upsetting rate and tool life decreased. Comparative example No. 6 is a case in which rolling was performed only in a temperature range of 1000° C. or higher and cooling was performed under appropriate cooling conditions, and corresponds to normal rolling. In this case, ferrite precipitation is insufficient and bainite structure occupies most of the structure. This is because ferrite transformation is not promoted since there is no rolling in the temperature range of 750 to less than 1000°C. As a result, the hardness is high, and the critical upsetting rate and tool life are low. Comparative Example No. 7 is a case where the rolling reduction ratio in the temperature range of 750 to less than 1000°C is as small as 30%. In this case No.6
Similarly, there is little ferrite generation and high hardness. Therefore, the marginal upsetting rate and tool life are low due to insufficient softening. The cooling method adopted in this example is as follows:
This method involves passing through a cooling chamber lined with ceramic fibers equipped with an electric heater and a cooling fan. As mentioned above, if the rolling conditions and cooling conditions are outside the limits set by the present invention, the hardness will be high, and the critical upsetting rate and tool life will be low, whereas if they are within the limits, hot rolling will continue. Steel with good cold forgeability and machinability could be produced. Example 2
【表】
第３表に示す組成の鋼Ｂ〜Ｆを溶製し、これら
のビレツトを第４表に示す圧延条件および冷却速
度（実施例１と同じ冷却手段を用いた）で製造し
た。仕上寸法は16mmφである。これら棒鋼の硬さ
及び圧縮試験における限界据込率を求めたとこ
ろ、第４表に示す結果となつた。[Table] Steels B to F having the compositions shown in Table 3 were melted and their billets were manufactured under the rolling conditions and cooling rates shown in Table 4 (using the same cooling means as in Example 1). The finished dimension is 16mmφ. When the hardness of these steel bars and the limit upsetting rate in compression tests were determined, the results are shown in Table 4.
【表】
第４表のNo.８〜10はいずれの成分組成において
も、軟化が十分に進行しており、限界据込率も高
く、良好な冷間鍛造性を有していた。
以上従来法によれば、構造用合金鋼線及び棒鋼
は熱間圧延材に軟化焼鈍処理を施した後に加工さ
れるので、軟化焼鈍のための設備が必要であるだ
けでなく、エネルギー的にもロスが多く、製造コ
スト、生産性の点でも問題があつたが、本発明に
よれば、従来方法による軟化焼鈍処理材と同等の
性能を有する鋼線・棒鋼を熱間圧延時の保有熱を
利用し、かつ生産性を損なうことなく経済的に得
ることができるので、産業上のメリツトは大き
い。[Table] Nos. 8 to 10 in Table 4 had sufficient softening in all component compositions, had a high limit upsetting rate, and had good cold forgeability. According to the conventional method, structural alloy steel wires and steel bars are processed after being subjected to softening annealing treatment on hot rolled materials, which not only requires equipment for softening annealing, but also consumes energy. There was a lot of loss, and there were also problems in terms of manufacturing costs and productivity, but according to the present invention, it is possible to reduce the retained heat during hot rolling of steel wires and bars that have the same performance as softened annealed materials by conventional methods. It has great industrial merits because it can be used and economically obtained without sacrificing productivity.
第１図はビレツトを1000℃以上で圧延したとき
の圧下率と硬さとの関係を示す図、第２図はビレ
ツトを1000℃未満で圧延したときの圧下率と硬さ
との関係を示す図である。
Figure 1 is a diagram showing the relationship between rolling reduction and hardness when a billet is rolled at 1000°C or higher, and Figure 2 is a diagram showing the relationship between rolling reduction and hardness when a billet is rolled at less than 1000°C. be.
Claims (1)
Mn0.3〜1.8wt％を含み、かつCr0.2〜1.5wt％、
Mo0.1〜0.8wt％およびNi0.3〜1.5wt％のうちか
ら選ばれる１種または２種以上を含有し、残部が
Feおよび不可避的不純物からなる鋼に対し、
1000℃〜1250℃の温度範囲で30〜80％の圧下率で
圧延するオーステナイト粒微細化のための第１段
圧延と、これに続く750〜1000℃未満の温度範囲
へ冷却し、該温度範囲内で50〜80％の圧下率で圧
延することによる、オーステナイト粒に歪を付与
するための第２段圧延とを施し、その後１℃／秒
以下の冷却速度で冷却することにより、フエライ
ト・パーライト組織とすることを特徴とする構造
用鋼線・棒鋼の直接軟化処理方法。1 C0.25~0.50wt%, Si0.10~0.50wt%,
Contains Mn0.3-1.8wt%, and Cr0.2-1.5wt%,
Contains one or more selected from Mo0.1-0.8wt% and Ni0.3-1.5wt%, with the remainder being
For steel consisting of Fe and unavoidable impurities,
The first stage rolling for austenite grain refinement involves rolling in a temperature range of 1000°C to 1250°C with a reduction ratio of 30 to 80%, followed by cooling to a temperature range of 750°C to less than 1000°C. Ferrite/pearlite is produced by rolling at a reduction rate of 50 to 80% in a second stage to impart strain to the austenite grains, and then cooling at a cooling rate of 1°C/sec or less. A method for direct softening treatment of structural steel wires and bars, characterized by forming a structure into a structure.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15392481A JPS5858235A (en) | 1981-09-30 | 1981-09-30 | Heat treatment for direct softening of steel wire and steel bar for structure |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15392481A JPS5858235A (en) | 1981-09-30 | 1981-09-30 | Heat treatment for direct softening of steel wire and steel bar for structure |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5858235A JPS5858235A (en) | 1983-04-06 |
| JPH0213004B2 true JPH0213004B2 (en) | 1990-04-03 |
Family
ID=15573057
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP15392481A Granted JPS5858235A (en) | 1981-09-30 | 1981-09-30 | Heat treatment for direct softening of steel wire and steel bar for structure |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5858235A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2015205305A (en) * | 2014-04-21 | 2015-11-19 | 大同特殊鋼株式会社 | Ring manufacturing method |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59100216A (en) * | 1982-11-29 | 1984-06-09 | Kawasaki Steel Corp | Manufacture of structural alloy steel for cold forging and for cutting |
| JPS59123741A (en) * | 1982-12-28 | 1984-07-17 | Kobe Steel Ltd | Hot-rolled high-tension wire rod requiring no heat treatment |
| JPS62188723A (en) * | 1986-02-14 | 1987-08-18 | Nippon Steel Corp | Manufacture of medium carbon steel for cold working having small deformation resistance |
| JPH03253514A (en) * | 1990-03-02 | 1991-11-12 | Nippon Steel Corp | Production of high-strength alloy steel having excellent cold workability |
| CN104561815B (en) * | 2013-10-09 | 2016-09-28 | 宝钢特钢有限公司 | A kind of high homogenizing big specification superhigh intensity rod iron and production method thereof |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5565324A (en) * | 1978-11-07 | 1980-05-16 | Sumitomo Metal Ind Ltd | Manufacture of low alloy steel excellent in cold workability |
-
1981
- 1981-09-30 JP JP15392481A patent/JPS5858235A/en active Granted
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5565324A (en) * | 1978-11-07 | 1980-05-16 | Sumitomo Metal Ind Ltd | Manufacture of low alloy steel excellent in cold workability |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2015205305A (en) * | 2014-04-21 | 2015-11-19 | 大同特殊鋼株式会社 | Ring manufacturing method |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5858235A (en) | 1983-04-06 |
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