Method for heat-treating a manganese steel product and manganese steel product

Patent metadata

Field	Value
Publication number	US-10450622-B2
Application number	US-201314653694-A
Country	US
Kind code	B2
Filing date	Dec 20, 2013
Priority date	Dec 21, 2012
Publication date	Oct 22, 2019
Grant date	Oct 22, 2019

Abstract

A method for heat treating a manganese steel product whose alloy comprises:
a carbon fraction (C) between 0.09 and 0.15 wt. %, and a manganese fraction (Mn) in the range of 3.5 wt. %≤Mn≤4.9 wt. %, the method comprising: performing a first annealing process (S 4.1 ) with the substeps
heating (E 1 ) the steel product to a first holding temperature (T 1 ), which lies above 780° C., holding (H 1 ) the steel product during a first time period (Δ 1 ) at the first holding temperature (T 1 ), cooling (A 1 ) the steel product,
performing a second annealing process (S 4.2 ) with the substeps
heating (E 2 ) the steel product to a holding temperature (T 2 ), which lies above 630° C. and below 660° C., holding (H 2 ) the steel product during a second time period (Δ 2 ) at the holding temperature (T 2 ), cooling (A 2 ) the steel product.

First claim

The invention claimed is:

1. Method for heat treating a manganese steel product: the method comprising the following steps:
providing a steel product, selected from the group consisting of a hot-rolled manganese steel product and a cold rolled manganese steel product, whose alloy comprises:
a carbon fraction (C) between 0.09 and 0.15 wt. %, and
a manganese fraction (Mn) in the range of 4.0 wt. %≤Mn≤4.9 wt. %, and
fractions of bainite microstructure,
performing a first annealing process (S 4 . 1 ) with the following substeps
heating (E 1 ) the steel product to a first holding temperature (T 1 ), which lies above 780° C.,
holding (H 1 ) the steel product during a first time period (Δ 1 ) at the first holding temperature (T 1 ) thereby allowing austenite (v) formation,
cooling (A 1 ) the steel product,

performing a second annealing process (S 4 . 2 ) with the following substeps
heating (E 2 ) the steel product to a holding temperature (T 2 ), which lies above 630° C. and below 660° C.,
holding (H 2 ) the steel product during a second time period (Δ 2 ) at the holding temperature (T 2 ) thereby allowing the formation of the two phases ferrite and austenite,
cooling (A 2 ) the steel product,
wherein the cooling (A 1 ; A 2 ) of the steel product during the first annealing process (S 4 . 1 ) and during the second annealing process (S 4 . 2 ) is carried out at a cooling rate which lies between 25 Kelvin/second and 200 Kelvin/second,
and wherein the second annealing process (S 4 . 2 ) is carried out subsequently to the first annealing process (S 4 . 1 ).

2. The method according to claim 1 wherein the first cooling of the steel product (A 1 ) and the second cooling of the steel product (A 2 ) are carried out at a cooling rate which lies between 40 Kelvin/second and 150 Kelvin/second.

3. The method according to claim 1 , wherein during the first annealing process (S 4 . 1 ) and during the second annealing process (S 4 . 2 ) the heating (E 1 ; E 2 ) is carried out at a heating rate which lies between 4 Kelvin/second and 50 Kelvin/second.

4. The method according to claim 1 , wherein the alloy additionally comprises:
a silicium fraction (Si),
an aluminium fraction (Al), and
a chromium fraction (Cr),

wherein the following relationship between the silicium fraction (Si), aluminium fraction (Al) and chromium fraction (Cr) holds: 0.3 wt. %≤Si+Al+Cr≤3 wt. %.

5. The method according to claim 4 , wherein
the chromium fraction (Cr) is always less than 0.4 wt. % and
the silicium fraction (Si) lies between 0.25 and 0.7 wt. %.

6. The method according to claim 5 , wherein the silicium fraction (Si) lies in the range of 0.3≤Si≤0.6.

7. The method according to claim 4 , wherein the following relationship between the silicium fraction (Si), aluminium fraction (Al) and chromium fraction (Cr) holds: 1.2 wt. %≤Si+Al+Cr≤2 wt. %.

8. The method according to claim 1 , wherein the alloy composition additionally comprises a nitrogen fraction (N) which lies in the range between 0.004 wt. % and 0.012 wt. %.

9. The method according to claim 8 , wherein the nitrogen fraction (N) lies in the range between 0.004 wt. % and 0.006 wt. %.

10. The method according to claim 1 , wherein during the first annealing process (S 4 . 1 ) the cooling (A 1 ) of the steel product is carried out so that the course of the temperature (T) of a corresponding cooling curve plotted over the time (t) passes through a region of bainite formation ( 50 ).

11. The method according to claim 1 , wherein by admixing or adding silicium (Si) and aluminium (Al) a region of bainite formation ( 50 ) during cooling (A 1 ) of the steel product is shifted in a direction of a more rapid cooling.

12. The method according to claim 1 , wherein the first time period (Δ 1 ) lies in the range of 3≤Δ 1 ≤10 minutes.

13. The method according to claim 12 , wherein the first time period (Δ 1 ) lies in the range of 4≤Δ 1 ≤5 minutes.

14. The method according to claim 1 , wherein the second time period (Δ 2 ) is in the range of 3≤Δ 2 ≤5 hours.

15. The method according to claim 14 , wherein the second time period (Δ 2 ) is in the range of 3.5≤Δ 2 ≤4.5 hours.

Assignees

• Voestalpine Stahl Gmbh

Inventors

• Arenholz Enno
• Samek Ludovic

Classifications

• C21D1/185

  from an intercritical temperature · CPC title

• C21D1/78

  Combined heat-treatments not provided for above · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/06

  containing aluminium · CPC title

• C21D1/26

  Methods of annealing · CPC title