High strength and high toughness cast steel material and method for producing the same

Patent metadata

Field	Value
Publication number	US-9797034-B2
Application number	US-201013498057-A
Country	US
Kind code	B2
Filing date	Sep 24, 2010
Priority date	Sep 25, 2009
Publication date	Oct 24, 2017
Grant date	Oct 24, 2017

Abstract

A high strength and high toughness cast steel material of the invention has a composition comprising 0.10 to 0.20% by mass of C, 0.10 to 0.50% by mass of Si, 0.40 to 1.20% by mass of Mn, 2.00 to 3.00% by mass of Ni, 0.20 to 0.70% by mass of Cr, and 0.10 to 0.50% by mass of Mo, and further comprising Fe and unavoidable impurities. The high strength and high toughness cast steel material of the invention is produced by subjecting an ingot having the above composition to annealing at 1,000 to 1,100° C., quenching at 850 to 950° C., tempering at 610 to 670° C., and then, if desired, stress-relief annealing at less than 610° C.

First claim

The invention claimed is:

1. A cast steel product comprising a cast steel material, which has a composition containing 0.14 to 0.20% by mass of C, 0.10 to 0.50% by mass of Si, 0.40 to 1.20% by mass of Mn, 2.42 to 3.00% by mass of Ni, 0.40 to 0.70% by mass of Cr, less than 0.004% by mass of Al, and 0.10 to 0.50% by mass of Mo, and further containing Fe and unavoidable impurities, wherein the cast steel material further comprises more than 90 ppm by mass and 150 ppm or less by mass of N as a compositional ingredient, and wherein the cast steel product has absorbed energy of 75 J or more measured by a Charpy impact test carried out using a test piece of V-notch according to JIS (Japanese Industrial Standard) No. 4 Test Piece and at a temperature of 0° C. and
wherein the cast steel material has a tensile strength of 620 MPa to 696 MPa.

2. The cast steel product according to claim 1 ,
wherein the product mass is 1 metric ton or more.

3. The cast steel product according to claim 1 , wherein the cast steel material further contains 0.05% by mass or less of V as a compositional ingredient.

4. The cast steel product according to claim 3 , wherein the cast steel material contains V in an amount of 0.02% by mass or more and 0.05% by mass or less.

5. The cast steel product according to claim 1 ,
wherein the cast steel material contains less than 0.01% by mass of Ti, 0.025% by mass or less of Sn, less than 0.015% by mass of P, and less than 0.015% by mass of S as the unavoidable impurities.

6. The cast steel product according to claim 1 , wherein Mn is present in a range of 0.40-0.54% by mass.

7. A method for producing a cast steel material, comprising:
a step of casting an ingot having a composition containing 0.14 to 0.20% by mass of C, 0.10 to 0.50% by mass of Si, 0.40 to 1.20% by mass of Mn, 2.20 to 3.00% by mass of Ni, 0.20 to 0.70% by mass of Cr, less than 0.005% by mass of Al, and 0.10 to 0.50% by mass of Mo, and further containing Fe and unavoidable impurities, wherein the composition of the ingot further comprises more than 80 ppm by mass and 150 ppm or less by mass of N,
an annealing step of performing a heat treatment at 1,000 to 1,100° C. on said ingot having said composition;
then a quenching step of performing a heat treatment at 850 to 950° C. on said ingot having said composition; and
then a tempering step of performing a heat treatment at 610 to 670° C. on said ingot having said composition,
wherein the annealing step and the quenching step each comprises a cooling step,
wherein in both cooling steps, cooling is performed at a cooling rate lower than that of cooling by liquid immersion,
wherein in the quenching step, cooling is performed at a cooling rate of about 300° C./hour, and
wherein the method does not include performing liquid cooling.

8. The method for producing a cast steel material according to claim 7 , further comprising a stress-relief annealing step of performing a heat treatment at less than 610° C. after the tempering step.

9. The method for producing a cast steel material according to claim 7 ,
wherein the composition of the ingot further satisfies the requirement that the ingot contains 0.05% by mass or less of V.

10. The method according to claim 9 , wherein the ingot contains 0.02% by mass or more and 0.05% by mass or less of V.

11. The method according to claim 7 , wherein the cast steel material has a tensile strength of 620 MPa or more.

12. The method according to claim 1 , wherein the ingot mass is 1 metric ton or more.

13. The method for producing a cast steel material according to claim 7 , wherein Mn is present in a range of 0.40-0.54% by mass.

Assignees

• Gotoh Yoshihiro
• Tanaka Shinji
• Azuma Tsukasa
• Japan Steel Works Ltd

Inventors

• Gotoh Yoshihiro
• Tanaka Shinji
• Azuma Tsukasa

Classifications

• C22C38/44 Primary

  with molybdenum or tungsten · CPC title

• C21D1/30

  Stress-relieving · CPC title

• C21D1/18

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title

• C22C38/46

  with vanadium · CPC title

• C21D6/00

  Heat treatment of ferrous alloys · CPC title