Method of manufacturing welded structure of ferritic heat-resistant steel and welded structure of ferritic heat-resistant steel

Patent metadata

Field	Value
Publication number	US-11167369-B2
Application number	US-201716325524-A
Country	US
Kind code	B2
Filing date	Sep 29, 2017
Priority date	Sep 30, 2016
Publication date	Nov 9, 2021
Grant date	Nov 9, 2021

Abstract

A method of manufacturing a welded structure of a ferritic heat-resistant steel is provided that prevents Type IV damage and that has good on-site operability without adding a high B concentration. The method includes: the step of preparing a base material including 8.0 to 12.0% Cr, less than 0.005% B and other elements; the step of forming an edge on the base material; a pre-weld heat treatment step in which a region located between a surface of the edge and a position distant from the surface of the edge by a pre-weld heat treatment depth of 30 to 100 mm is heated to a temperature of 1050 to 1200° C. and is held at this temperature for 2 to 30 minutes; a welding step in which the edge is welded to form the weld metal; and a post-weld heat treatment step in which a region located between the surface of the edge and a position distant from the surface of the edge by a distance not smaller than the pre-weld heat treatment depth and not greater than 100 mm is heated to a temperature of 720 to 780° C. and is held at this temperature for a time period not shorter than 30 minutes and satisfying the following formula, (1):(Log(t)+12)·(T+273)<13810  (1).

First claim

The invention claimed is:

1. A method of manufacturing a welded structure of a ferritic heat-resistant steel including a base material, a weld heat-affected zone and a weld metal, comprising:
the step of preparing the base material, the base material having a chemical composition including, in mass %:
0.05 to 0.12% C;
0.02 to 0.45% Si;
0.40 to 0.80% Mn;
8.0 to 12.0% Cr;
0.003 to 0.080% N;
0.30 to 1.30% Mo;
0.005 to 0.10% Nb;
0.005 to 0.50% V;
0 to 2.0% W;
0 to 3.5% Re;
0 to 0.15% Ti;
0 to 0.15% Zr;
0 to 0.0050% Ca;
0 to 0.0050% Mg;
0 to 0.0500% Y;
0 to 0.0500% Ce; and
0 to 0.0500% La,
Ni being limited to below 0.20%,
Cu below 0.20%,
B below 0.005%,
Al below 0.025%,
P below 0.020%,
S below 0.010%, and
O below 0.010%,
the balance being Fe and impurities;
the step of forming an edge on the base material;
a pre-weld heat treatment step in which a region located between a surface of the edge and a position distant from the surface of the edge by a pre-weld heat treatment depth of 30 to 100 mm is heated to a temperature of 1050 to 1200° C. and is held at this temperature for 2 to 30 minutes;
a welding step in which, after the pre-weld heat treatment step, the edge is welded to form the weld metal; and
a post-weld heat treatment step in which, after the welding step, a region located between the surface of the edge and a position distant from the surface of the edge by a distance not smaller than the pre-weld heat treatment depth and not greater than 100 mm is heated to a temperature of 720 to 780° C. and is held at this temperature for a time period not shorter than 30 minutes and satisfying the following formula, (1):
(Log( t )+12)·( T+ 273)<13810  (1),

where t is the holding time and T is the temperature; the unit of t is hour and the unit of T is ° C.; and Log is the common logarithm.

2. The method of manufacturing a welded structure of a ferritic heat-resistant steel according to claim 1 , wherein the pre-weld heat treatment step is performed in two or more divided sub-steps.

3. The method of manufacturing a welded structure of a ferritic heat-resistant steel according to claim 1 , wherein an average grain size of M 23 C 6 -type carbides precipitated on large-angle grain boundaries of the weld heat-affected zone is not greater than 300 nm, each of the large-angle grain boundaries being a grain boundary with an angle relative to an adjacent crystal grain of 15° or larger,
an average inter-particle-surface distance of the M 23 C 6 -type carbides on the large-angle grain boundaries is not greater than 200 nm, and
a coverage of the large-angle grain boundaries with the M 23 C 6 -type carbides is not smaller than 40%, and
wherein M in the M 23 C 6 -type carbides is one or more of Cr, Fe, Mo and W in a total of 70 atom % or more.

4. The method of manufacturing a welded structure of a ferritic heat-resistant steel according to claim 1 , wherein the base material has a chemical composition including one or two selected from the group consisting of, in mass %:
1.5 to 2.0% W; and
0.5 to 3.5% Re.

5. The method of manufacturing a welded structure of a ferritic heat-resistant steel according to claim 1 , wherein the base material has a chemical composition including one or two selected from the group consisting of, in mass %:
0.005 to 0.15% Ti; and
0.005 to 0.15% Zr.

6. The method of manufacturing a welded structure of a ferritic heat-resistant steel according to claim 1 , wherein the base material has a chemical composition including one or more selected from the group consisting of, in mass %:
0.0003 to 0.0050% Ca;
0.0003 to 0.0050% Mg;
0.0100 to 0.0500% Y;
0.0100 to 0.0500% Ce; and
0.0100 to 0.0500% La.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Hasegawa Yasushi
• Okada Hirokazu

Classifications

• C22C38/48

  with niobium or tantalum · CPC title

• B23K15/00

  Electron-beam welding or cutting · CPC title

• C22C38/42

  with copper · CPC title

• C22C38/00

  Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) · CPC title

• C22C38/44 Primary

  with molybdenum or tungsten · CPC title