Hot-work die steel and a preparation method thereof

Patent metadata

Field	Value
Publication number	US-2021363603-A1
Application number	US-202017021404-A
Country	US
Kind code	A1
Filing date	Sep 15, 2020
Priority date	May 20, 2020
Publication date	Nov 25, 2021
Grant date	—

Abstract

The present application provides a hot-work die steel and a preparation method thereof, wherein the chemical constituents of the hot-work die steel in mass percentage are as follows: C: 0.20-0.32 wt %, Si: ≤0.5 wt %, Mn: ≤0.5 wt %, Cr: 1.5-2.8 wt %, Mo: 1.5-2.5 wt %, W: 0.5-1.2 wt %, Ni: 0.5-1.6 wt %, V: 0.15-0.7 wt %, Nb: 0.01-0.1 wt %, and a balance of iron, wherein an alloying degree is 5-7%; a tensile strength of the hot-work die steel at 700° C. is 560-700 MPa; a value of hardness of the hot-work die steel at room temperature is 32-38 HRC after holding at 700° C. for 3-5 h; and the hot-work die steel has an elongation of 14% to 16% at room temperature, a percentage reduction of area of 48% to 65%, and an impact toughness of 52-63 J at room temperature. The hot-work die steel of the present application has an excellent thermal stability as well as a good plasticity and a toughness at room temperature.

First claim

1 . A hot-work die steel, comprising the following chemical constituents:
C: 0.20-0.32 wt %, Si: ≤0.5 wt %, Mn: ≤0.5 wt %, Cr: 1.5-2.8 wt %, Mo: 1.5-2.5 wt %, W: 0.5-1.2 wt %, Ni: 0.5-1.6 wt %, V: 0.15-0.7 wt %, Nb: 0.01-0.1 wt %, and a balance of iron, wherein an alloying degree is 5-7 wt %; wherein a tensile strength of the hot-work die steel at 700° C. is 560-700 MPa; wherein a value of hardness of the hot-work die steel at room temperature is 32-38 HRC after holding at 700° C. for 3-5 h; and wherein the hot-work die steel has an elongation of 14% to 16% at room temperature, a percentage reduction of area of 48% to 65% at room temperature, and an impact toughness of 52-63 J at room temperature.

2 . The hot-work die steel according to claim 1 , wherein the hot-work die steel further comprises at least one of the following chemical constituents:
Zr: 0.01-0.03 wt %, Co: 0.10-0.50 wt %, B: 0.001-0.005 wt %, Re: 0.01-0.10 wt %, Ti: 0.02-0.06 wt %, and Y: 0.01-0.1 wt %.

3 . The hot-work die steel according to claim 1 , wherein the hot-work die steel comprises less than 0.02 wt % of S and less than 0.02 wt % of P.

4 . The hot-work die steel according to claim 1 , wherein the hot-work die steel comprises a tempered sorbite structure that retains lath characteristics after the hot-work die steel is stretched at 700° C.

5 . The hot-work die steel according to claim 1 , wherein the hot-work die steel comprises a nanoscale acicular alloy carbide after the hot-work die steel is stretched at 700° C.

6 . The hot-work die steel according to claim 5 , wherein the nanoscale acicular alloy carbide is: V 0.5-0.8 Mo 0.5-0.6 Cr 0.15-0.3 W 06-0.14 Nb 0.01-0.02 C.

7 . (canceled)

8 . A method for producing the hot-work die steel according to claim 1 , comprising the following steps:
a smelting step: preparing a raw material according to the following mass percentages:
C: 0.20-0.32 wt %, Si: ≤0.5 wt %, Mn: ≤0.5 wt %, Cr: 1.5-2.8 wt %, Mo: 1.5-2.5 wt %, W: 0.5-1.2 wt %, Ni: 0.5-1.6 wt %, V: 0.15-0.7 wt %, Nb: 0.01-0.1 wt %, and a balance of iron,
processing the raw material into an electrode rod by arc smelting, secondary refining, vacuum degassing, and forging in a forging furnace; an electroslag remelting step: removing an oxidized layer of the electrode rod, then introducing the electrode rod into a vacuum electroslag remelting device for secondary refining, keeping a temperature of water in the water cooling system of the electroslag remelting device not higher than 70° C., and obtaining an electroslag ingot by electroslag remelting from the electrode rod, wherein a melting rate is 7-12 kg/min, and a temperature of a cooling water of a crystallizer is held at 40-50° C.; a homogenizing annealing step: heating the electroslag ingot to 1200-1250° C. and holding for 15-23 h; a forging step: cooling the electroslag ingot to a forging heating temperature of 1150-1200° C. and then forging to obtain an ingot, wherein an initial forging temperature is 1130 to 1160° C., and a final forging temperature is ≥850° C.; an annealing after forging step: introducing the ingot into an annealing furnace after the temperature of the ingot is lower than 500° C., heating to 830-890° C. at a heating rate not more than 100° C./h, holding for [120 min+r (mm)×2 min/mm] or [120 min+d (mm)/2×2 min/mm], lowering the temperature to below 500° C. at a cooling rate of 20-40° C./h, taking the ingot out from the annealing furnace and air-cooling to obtain an annealed ingot; a heat treatment of fine grain step: heating the annealed ingot to 930-1150° C. and performing a first holding for a first holding time of [(15-40) min+r (mm)×2 min/mm] or [(15-40) min+d (mm)/2×2 min/mm], water cooling to 400-500° C. within 1-2 min, then air cooling to 250-280° C. and performing a second holding for a second holding time of 5-10 h; and then holding at a temperature of 660-700° C. for 5-10 h; a tempering treatment step: heating the held ingot to 980-1100° C. and holding for [(15-40) min+r (mm)×2 min/mm] or [(15-40) min+d (mm)/2×2 min/mm], then quenching to 50-150° C., and then tempering at 580-660° C. for 6-16 h to obtain the hot-work die steel; wherein r is a radius of the material and d is a thickness of the material.

9 . The method for producing the hot-work die steel according to claim 8 , wherein the raw material further comprises at least one of the following constituents: Zr: 0.01-0.03 wt %, Co: 0.10-0.50 wt %, B: 0.001-0.005 wt %, Re: 0.01-0.10 wt %, Ti: 0.02-0.06 wt %, and Y: 0.01-0.1 wt %.

10 . The method for producing the hot-work die steel according to claim 8 , wherein the forging step includes:
forming and forging by means of a precision forging machine, wherein the forging heating temperature is 900-1050° C., the initial forging temperature is 850-950° C., and the final forging temperature is ≥800° C.; alternatively, forming and forging by a hydraulic hammer or oil hydraulic press, wherein the forging heating temperature is 1150-1200° C., the initial forging temperature is 1130-1160° C., and the final forging temperature is ≥850° C.

11 . The method for producing the hot-work die steel according to claim 8 , wherein the holding time of the annealing after forging step is 6-8 h.

12 . The hot-work die steel according to claim 1 , wherein the tensile strength of the hot-work die steel at 700° C. is 600-700 MPa.

Assignees

• Univ Beijing Science & Technology

Inventors

• Huang Jinfeng
• Zhang Jin
• Zhang Cheng
• Zhao Chao
• Lian Yong
• Li Jianqiang
• Zhang Cheng

Classifications

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C21D1/78

  Combined heat-treatments not provided for above · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• C22C38/54

  with boron · CPC title

• C22C38/04

  containing manganese · CPC title