AU2018393178B2

AU2018393178B2 - Method for fabricating low-cost, short-production-cycle wear-resistant steel

Info

Publication number: AU2018393178B2
Application number: AU2018393178A
Authority: AU
Inventors: Zaiwei JIANG; Jianfeng JIN; Tong Liu; Bo Ning; Sicong WANG; Qiangjun YAN; Liu Yang
Original assignee: Nanjing Iron and Steel Co Ltd
Current assignee: Nanjing Iron and Steel Co Ltd
Priority date: 2017-12-25
Filing date: 2018-08-31
Publication date: 2021-07-08
Anticipated expiration: 2038-08-31
Also published as: WO2019128286A1; ZA202004537B; CN108179350A; AU2018393178A1; CN108179350B

Abstract

The present invention provides a method for fabricating a low-cost, short-production-cycle wear-resistant steel; the composition of the wear-resistant steel, by mass percentage, is: C: 0.10-0.20%; Si: 0.20-0.30%; Mn: 1.10-1.50%; Cr: 0.15-0.25%; Mo: 0.10-0.30%; Nb: 0.01-0.02%; Ti: 0.01-0.03%; B: 0.0015-0.0020%; S: ≤0.0012%; P: ≤0.015%; O: ≤0.01%; N: ≤0.005%; the remainder is Fe. After the cast strand is hot-rolled, the steel plate is quenched at 920°C, then directly straightened with no need for thermal tempering; it is thus possible to obtain a steel plate having a lower residual stress value of NM 400, which is comparable to the residual stress value of a steel plate after using quenching, tempering, and straightening processes. The present invention uses quenching and direct straightening processes to produce a wear-resistant steel NM 400 plate; no intermediate tempering is required, thus reducing the process steps, decreasing cost, and shortening the production cycle.

Description

Method for Fabricating Low-Cost, Short-Production-Cycle Wear-Resistant Steel

TECHNICAL FIELD

The present invention pertains to the technical field of iron and steel, and relates to a method for manufacturing wear-resistant steel, specifically to a method for fabricating wear-resistant steel NM400 by quenching and direct straightening processes.

BACKGROUND ART

Wear-resistant steel is a special material that is widely used in engineering. Owing to its good wear resistance, it is mostly used in places where wear occurs with ore, rock, soil and sand. Wear-resistant steel is often made into engineering machinery, mining machinery, coal mining machinery, crushers and other mechanical parts. The traditional wear-resistant steel NM400 is quenched + tempered + straightened after hot rolling to fully eliminate the residual stress, resulting in more process steps, a high cost and a long production cycle.

SUMMARY OF THE INVENTION

The technical problem that the present invention intends to solve is to provide a method for fabricating low-cost, short-production-cycle wear-resistant steel to overcome the defects existing in the prior art. The present invention realizes production of a wear-resistant steel NM400 plate by the quenching and direct straightening processes with no need for intermediate tempering treatment, thereby reducing the process steps, decreasing cost, and shortening the production cycle. The obtained NM400 steel plate has a low residual stress value, which is comparable to the residual stress value of a steel plate after using quenching, tempering, and straightening processes.

The present invention adopts the following technical solution to solve the foregoing technical problem:

A method for fabricating low-cost, short-production-cycle wear-resistant steel, comprising the following steps:

(I) Smelt and cast into strand: The composition of the wear-resistant steel, by mass

Description

percentage, is: C: 0.10-0.20%; Si: 0.20-0.30%; Mn: 1.10-1.50%; Cr: 0.15-0.25%; Mo: 0.10-0.30%; Nb: 0.01-0.02%; Ti: 0.01-0.03%; B: 0.0015-0.0020%; S<0.0012%; P<0.015%; 0<0.01%; N<0.005%; the remainder is Fe;

(II) The cast strand is sent into a heating furnace and heated at 1,150-1,200°C in three sections, including 500±20°C in the preheating section, 1,200±20°C in the heating section and 1,180±20°C in the soaking section, the temperature holding time is 3-6 hours, and after tapping, it is rolled on a heavy and medium plate mill for multiple passes into the finished thickness; and

(III) The rolled steel plate is sent into a quenching machine and quenched at 920°C, and the quenched steel plate is directly sent into a straightening machine without tempering and is straightened to eliminate residual stress.

The composition design of the present invention is based on the following principle:

C has a bearing on the strength, hardness and hardenability of the steel. With the increase of carbon content, the yield point and tensile strength increase, but the plasticity and impact resistance decrease. High carbon content will also reduce the atmospheric corrosion resistance of the steel and undermine the wear resistance of the steel, so low carbon is set for wear-resistant steel.

Mn improves the toughness, strength, hardness, wear resistance, hardenability and hot workability of the steel. Manganese can strengthen ferrite and has an effect of solution strengthening, especially in low-alloy general structural steel. Manganese reduces the driving force of phase transition and shifts the C curve to the right, so it improves the hardenability of the steel. However, Mn is an overheat-sensitive element. When the heating temperature is too high during quenching, coarse grains may be caused; Mn has a large segregation coefficient during solidification and is liable to segregation at the grain boundary, generating an ill impact on performance and leading to increase in the amount of residual austenite in the steel quenching structure, so the content of manganese in low-alloy wear-resistant steel is controlled between 1.0-2.0%.

Si is a ferrite forming element and has a strong solution strengthening effect, thereby improving the strength of the steel. Silicon prevents carbide nucleation and growth, shifts the C curve to the right and improves the hardenability of the steel. Silicon inhibitsc-K nucleation, growth and transformation and can improve the low temperature tempering

Description

stability of the steel, but too high silicon content will significantly reduce the plasticity, toughness and ductility of the steel.

Cr reduces the driving force of phase transition, and also reduces carbide nucleation and growth during the phase transition, thereby improving the hardenability of the steel. Chromium is a performance element of carbides, and the structure grows in M3C type during tempering to improve the stability of tempering. Chromium carbides are relatively stable, not easy to grow, can refine grains, and improve carbide uniformity. Chromium is a main element of stainless steel. Chromium is a ferrite forming element, raises the Al point and increases the quenching temperature, thereby improving thermal fatigue.

Ni can increase the strength of the steel while maintaining good plasticity and toughness. Nickel has high wear resistance to acid and alkali, and is rusting and heat resistant at high temperature. However, since nickel is a scarce resource, other alloy elements should be used instead of nickel-chromium steel as far as possible.

Ti mainly exists in the form of carbides TiN and TiC in steel. Main roles of Ti: (1) Refine the structure and grains of the steel and increase the grain coarsening temperature; (2) When dissolved in austenite at high temperature, it improves the hardenability of the steel, on the contrary, if it exists in the form of carbides, it will reduce the hardenability of the steel; (3) Improve the tempering stability of quenched steel and produce a secondary hardening effect.

Mo effectively suppresses the segregation of harmful elements in steel and is an effective element to eliminate or mitigate the tempering brittleness of steel at high temperature. Molybdenum is a strong carbide-forming element and reduces the carbon activity in the steel, and its carbides are stable and are not easy to grow, so molybdenum can refine grains and improve the tempering stability of the steel. Molybdenum can form MoO3, an oxide containing Mo, which is compact and stable, improving the corrosion resistance of the steel in non-oxidizing acids, and effectively preventing pitting corrosion.

Nb can refine grains, increase the grain coarsening temperature, reduce the overheating sensitivity and temper brittleness of the steel, and under certain conditions, increase the strength, toughness and creep resistance of the steel;

A trace amount of B can be adsorbed on the austenite grain boundary to reduce the energy of the grain boundary and improve the hardenability of the steel. Air-cooled bainite steel can be obtained with presence of Mn. Rare earth can not only effectively refine the

Description

as-cast structure, purify the grain boundary, improve the morphology and distribution of carbides and inclusions and enable the low-alloy wear-resistant steel to maintain sufficient resilience elements (RE) but also can remove oxygen, sulfur and harmful impurities, refine grains, reduce the segregation of dendrites, improve toughness and raise steel quality.

Beneficial effects of the present invention: The present invention realizes production of wear-resistant steel NM400 plates by the quenching and direct straightening processes with no need for intermediate tempering treatment, thereby reducing the process steps, decreasing cost, and shortening the production cycle; by the quenching and direct straightening processes, the present invention can obtain NM400 steel plates with a low residual stress value, which is equivalent to the residual stress value of the steel plates obtained from the quenching, tempering and straightening processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process route map of the present invention.

DETAILED DESCRIPTION

Embodiment 1

This embodiment is a method for fabricating low-cost, short-production-cycle wear-resistant steel. The process route is as shown in FIG. 1. The design composition of the wear-resistant steel of this embodiment in weight percentage is: C: 0.15%; Si: 0.25%; Mn: 1.37%; Cr: 0.19%; Mo: 0.20%; Nb: 0.015%; Ti: 0.02%; B: 0.0013%; S: 0.0011%; P: 0.012%; 0: 0.008%; N: 0.005%; the remainder is Fe.

Converter steelmaking and continuous casting into strand were adopted according to the foregoing composition. The temperature of the heating furnace was 1,200°C, the heating was in three sections, including 500±20°C in the preheating section, 1,220±20°C in the heating section and 1,200±20°C in the soaking section, the temperature holding time was 5 hours, and after tapping, it was rolled on a heavy and medium plate mill for multiple passes at two stages including rough rolling and finish rolling into the finished thickness 6mm. The rolled steel plate was sent into a quenching machine and quenched at 920°C, and the quenched steel plate was directly straightened with no need for intermediate tempering. In the end, the magnetic

Description

hysteresis nondestructive testing and evaluation instrument was used to measure the residual stress, which is compared to the wear-resistant steel produced by the quenching, tempering, and straightening processes. The yield strength was 1,215MPa, tensile strength was 1,240MPa, A50 elongation was 22%, surface Brinell hardness was 420HBW, Charpy impact energy at -20°C was 38, 36, 39J, and the performance met the technical requirements of national standard GB/T24186- 2009.

Table 1 is the comparison of residual stress under temper straightening and direct straightening processes. It can be seen that the residual stress value of the direct straightening process is comparable to that of the temper straightening process.

Table 1 Comparison of residual stress under temper straightening and direct straightening processes

No. Treatment process Residual stress valueG/MPa

1 Temper straightening 37.6

2 Direct straightening 38.9

Embodiment 2

This embodiment is a method for fabricating low-cost, short-production-cycle wear-resistant steel. The process route is as shown in FIG. 1. The design composition of the wear-resistant steel of this embodiment in weight percentage is: C: 0.14%; Si: 0.26%;Mn: 1.24%; Cr: 0.22%; Mo: 0.14%; Nb: 0.012%; Ti: 0.018%; B: 0.0017%; S: 0.0007%; P: 0.010%; 0: 0.007%; N: 0.005%; the remainder is Fe.

Converter steelmaking and continuous casting into strand were adopted according to the foregoing composition. The temperature of the heating furnace was 1,180°C, the heating was in three sections, including 500±20°C in the preheating section, 1,220±20°C in the heating section and 1,200±20°C in the soaking section, the temperature holding time was 5 hours, and after tapping, it was rolled on a heavy and medium plate mill for multiple passes at two stages including rough rolling and finish rolling into the finished thickness 16mm. The rolled steel plate was sent into a quenching machine and quenched at 920°C, and the quenched steel plate was directly straightened with no need for intermediate tempering. In the end, the magnetic hysteresis nondestructive testing and evaluation instrument was used to measure the residual

Description

stress, which is compared to the wear-resistant steel produced by the quenching, tempering, and straightening processes. The yield strength was 1,21OMPa, tensile strength was 1,235MPa, A50 elongation was 20%, surface Brinell hardness was 418HBW, Charpy impact energy at -20°C was 35,40,38J, and the performance met the technical requirements of national standard GB/T24186- 2009.

Table 2 is the comparison of residual stress under temper straightening and direct straightening processes. It can be seen that the residual stress value of the direct straightening process is comparable to that of the tempering straightening process.

Table 2 Comparison of residual stress under temper straightening and direct straightening processes

No. Treatment process Residual stress value a/MPa 1 Temper straightening 36.8

2 Direct straightening 37.4

In addition to the foregoing embodiments, the present invention may have other implementation manners. All the technical solutions formed from adoption of identical replacements or equivalent changes are within the scope of protection required by the present invention.

Claims

Claims 1. A method for fabricating low-cost, short-production-cycle wear-resistant steel, comprising the following steps:

(I) Smelt and cast into strand: The composition of the wear-resistant steel, by mass percentage, is: C: 0.10-0.20%; Si: 0.20-0.30%; Mn: 1.10-1.50%; Cr: 0.15-0.25%; Mo: 0.10-0.30%; Nb: 0.01-0.02%; Ti: 0.01-0.03%; B: 0.0015-0.0020%; S<0.0012%; P<0.015%; 0<0.01%; N<0.005%; the remainder is Fe;

(II) The cast strand is sent into a heating furnace and heated at 1,150-1,200°C in three sections, including 500±20°C in the preheating section, 1,200±20°C in the heating section and 1,180±20°C in the soaking section, the temperature holding time is 3-6 hours, and after tapping, it is rolled on a heavy and medium plate mill for multiple passes into the finished thickness; and

(III) The rolled steel plate is sent into a quenching machine and quenched at 920°C, and the quenched steel plate is directly sent into a straightening machine without tempering and is straightened to eliminate residual stress.
2. The method for fabricating low-cost, short-production-cycle wear-resistant steel according to claim 1, wherein the composition of the wear-resistant steel, by mass percentage, is: C: 0.15%; Si: 0.25%; Mn: 1.37%; Cr: 0.19%; Mo:0.20%; Nb: 0.015%; Ti: 0.02%; B: 0.0013%; S: 0.0011%; P: 0.012%; 0: 0.008%,; N: 0.005%; the remainder is Fe.
3. The method for fabricating low-cost, short-production-cycle wear-resistant steel according to claim 1, wherein the composition of the wear-resistant steel, by mass percentage, is: C: 0.14%; Si: 0.26%; Mn: 1.24%; Cr: 0.22%; Mo: 0.14%; Nb: 0.012%; Ti: 0.018%; B: 0.0017%; S: 0.0007%; P: 0.010%; 0: 0.007%; N: 0.005%; the remainder is Fe.
4. The method for fabricating low-cost, short-production-cycle wear-resistant steel according to claim 2, comprising the following steps:

(I) Smelt according to the composition and cast into strand;

(II) The cast strand is sent into a heating furnace and heated at 1,200°C in three sections, including 500±20°C in the preheating section, 1,220±20°C in the heating section and 1,200±20°C in the soaking section, the temperature holding time is 5 hours, and after tapping, it is rolled on a heavy and medium plate mill for multiple passes at two stages including rough rolling and finish rolling into the finished thickness 6mm; and

Claims (III) The rolled steel plate is sent into a quenching machine and quenched at 920°C, and the quenched steel plate is directly sent into a straightening machine without tempering and is straightened to eliminate residual stress.
5. The method for fabricating low-cost, short-production-cycle wear-resistant steel according to claim 3, comprising the following steps:

(I) Smelt according to the composition and cast into strand;

(II) The cast strand is sent into a heating furnace and heated at 1,180°C in three sections, including 500±20°C in the preheating section, 1,200±20°C in the heating section and 1,180±20°C in the soaking section, the temperature holding time is 5 hours, and after tapping, it is rolled on a heavy and medium plate mill for multiple passes at two stages including rough rolling and finish rolling into the finished thickness 16mm; and

(III) The rolled steel plate is sent into a quenching machine and quenched at 920°C, and the quenched steel plate is directly sent into a straightening machine without tempering and is straightened to eliminate residual stress.

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FIG. 1

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